For this prompt at comment_fic: 'MCU, Avengers team, the rest of the Avengers moving into Stark Tower, finally.'
This is a Tony-centric, internal POV fic, so everyone else listed is just mentioned.
Tony thinks it makes no sense for them to waste time converging from extreme edges of the globe whenever something explodes or mutates or goes to hell, even if some of them can cover distances at a mind-boggling pace. They should just be in roughly the same ten mile radius so all they have to do is hop on a plane and fly to wherever the trouble is together. It conserves fuel, saves time, and probably builds team morale (or something like that). And since no one else is stepping up to collect them, he takes it upon himself to get it done. The part where he's the only one with the resources to do it is entirely beside the point.
Banner is first, in that Tony invites him over several times to work on projects, and eventually he just never leaves. Four of the floors have apartments; Pepper talks him into taking a studio one night over a blackberry slump and fresh sweet cream ice cream. Banner blames his acquiescence on the dessert for the next few days, and says it's hard for him to sleep in the city, but by the end of the first week he's abandoned that line and a month in he's looking more relaxed than Tony's ever seen him.
At first he has just a Murphy bed, a flat screen TV and DVD player, a computer, and a few bookshelves. All the years on the move have convinced him to decorate sparingly. But as the days go by he starts adding to the walls; art tiles, paintings, hangings, pictures. It takes six months for him to invest in personal cookware, and when he does, Tony's reasonably sure he's not going anywhere any time soon. (Tony won't admit out loud that Banner feeling comfortable enough to put things on the wall and buy himself dishes eases something inside him that's been tight and knotted up.)
Thor is the next to arrive, which happens when Tony offers a contract to Jane Foster to come and work on deep space probes and whatever else she feels like. Tony isn't actually fishing for Thor, he just wants Foster, because she's the best there is and SpaceX isn't interested in anything less than that for this project. She also has data taken directly from the Greenwich event, which will no doubt go a long way to helping her build wormhole technology. That has the potential to change life on Earth, and Tony will be damned if he's not involved with humanity's first steps in interstellar travel somehow, even if it's just as Foster's landlord. Thor showing up with her would merely be a super convenient bonus.
That's assuming he's around, though, which he and Bruce don't really know when they decide to make the offer to Foster. Tony's mostly sure he is—he's seen the footage of the Greenwich event in all its fuzzy, smartphone-quality, distorted glory—but it would be nice to have confirmation. Foster, however, doesn't want to discuss Thor, at all. She doesn't have Hill or Romanoff's finesse for lying, but she can change a subject with the best of them. So they dance around that tantalizing question and its elusive answer while they sort out the terms of her contract, setting down dates and making reservations, only to ramp it all up when SHIELD and Hydra have a shootout in front of the whole world on international television. Tony pats himself on the back only a little bit when Thor steps off the Stark Industries helicopter looking like someone trying to pretend to be human in jeans and a button-down shirt.
Foster has brought with her a small library, several crates of equipment, her laptop, and some personal effects. Thor has brought his magic space hammer, a few sets of human clothes, and nothing else, which really disappoints Tony. He'd been hoping for a few outer space knickknacks, maybe a fascinating house plant or mythical pet (wasn't he supposed to have goats?), but no. For the Prince of an entire world, he travels pretty light. Even his armor is nowhere to be seen, though when Tony asks Thor assures him he has it handy. That's when Tony realizes that, along with language magic, Asgardians also have clothing magic, and damn if that's not the best thing ever. Forget altering the weather or not aging; this is functional in a way anyone can appreciate. Need a clean suit for that board meeting? Presto! Don't want to move a closetful of shoes when you get a new place? Presto! Tired of losing half of your socks to a ravenous dryer? Presto!
Thor demonstrates how his armor works after Tony pesters him enough ('distance' and 'space' magic, he calls it), but indicates he wouldn't be able to teach Tony how to use it. Tony sulks for an entire afternoon. He also explains to Pepper at great length that he isn't jealous of how along with amazing, world-altering magic, Thor also has practical, down-to-earth 'space saver' magic that simplifies his every day life. Pepper flat out says she is jealous, and is no-doubt thinking about how Tony has already filled three labs with his own personal side projects which will in all likelihood go nowhere.
Rogers and Sam Wilson (of the US Air Force's Falcon project) swing by the Tower after they've recovered from turning world espionage on its head. Since they both already have their own apartments it takes some work to convince them to agree to a place, but their current plans help in that regard. They have someone to track down, which they expect to take a while, and they won't be around except when prepping for more searching. Seeing as Tony will only charge them nominal rent, space in the Tower is a better use of their money, plus more secure than leaving their apartments empty for weeks on end.
The person they're looking for is none other than the guy with the metal arm who Tony saw shooting up Washington, D.C. on traffic camera feeds. He is, apparently, a notorious assassin with a half-century long legacy, and also one of Rogers' old war buddies. It's a complex story which Rogers explains in a handful of terse, unilluminating sentences. Tony can't help but wonder if looking for this guy is actually a good idea, because if he's a former assassin who's decided to lie low then maybe they should just let him do that. But before he can voice this opinion Rhodey gives him the world's Most Meaningful and Least Subtle Look ever, and he lets the subject drop.
Rogers and Wilson expect their layovers will be just a few days here and there, so they take a single, modest, two-person unit, and don't put much in it—clothes, some framed pictures, some books. They add to this collection as they come and go, and it stops looking like a college dorm room belonging to two seniors too involved with their thesis to ever be in it. Tony and Rhodey hammer out some improvements for the Falcon wings, and rope Wilson in once they have something to show him. He's ecstatic, especially with the color, because as it turns out he likes red too.
Over the course of the next few months the time Wilson and Rogers are gone shrinks and the time they stay grows, and they start going on missions with the rest of them. There are Hydra cells, various powerful people SHIELD has pissed off who don't feel the need to tread lightly anymore, deep sea monsters, and who knows what else to deal with. Wilson is a fabulous addition, especially since it's not always possible for Rhodey to join them.
It gradually becomes clear Rogers' friend isn't going to just sit out in plain sight and wait for them to find him. Tony points out that if they can convince Romanoff and Barton to show up their chances of locating him will go up exponentially, especially since former Deputy Director of SHIELD Maria Hill is an employee of Stark Industries. The three of them working together can probably find Barnes—that's the friend's name—sooner rather than later.
Wilson and Rogers have a long conversation out on the deck, then come inside and agree to the plan. Hill, who of course has been in contact with Romanoff the entire time (Tony had known hiring a former spy was going to be an adventure), sends off a message via whatever back channels she still has. A few hours later she says Romanoff and Barton will arrive when they arrive.
It's a little tense until they do, because Rogers is really worked up about any pause in looking for Barnes. Thor is super helpful here, both as a distraction by asking Rogers to show him New York like a proper New Yorker, and in training with him while Wilson and Rhodey and Tony work on the new wings. Thor and Rogers' excursions produce more things for the apartment Rogers and Wilson are sharing, and it starts looking more like it should. Soon there's a modest stereo and two iPods with collections of music, a wider variety of books, and various trinkets from around the city. Eventually they even get a TV.
Romanoff and Barton arrive on a Saturday bearing donuts, coffee, and a jump drive for Rogers and Wilson. Neither of them are interested in permanent living spaces, which Tony was expecting because Hill hadn't wanted a place either. Instead, they take studios and turn them into deluxe crash pads for cleaning up up and taking a breather after a mission. Barton's never really evolves beyond that, not really; he's just too cagey after Loki and the Tesseract. Wherever he lives, it's not in the Tower, and he doesn't answer questions about it. Tony works out that it's somewhere in the city, so he doesn't push. Pushing ex-spy-assassins is always a bad idea.
Interestingly, Romanoff outfits her unit properly, and the decor doesn't seem to be for show either. There's too many personal touches in what she's chosen for furniture and put on the walls: movie posters (old 30s and 40s nostalgia, mostly), some framed photographs and postcards, an oak and walnut side table by the window, and an old, black, wrought iron and creamy red marble vanity in the bathroom. Tony figures out that he's just added to her no-doubt extensive bolt hole network, and can't help but find the number of ex-spies he's subletting to morbidly amusing.
Hill, Romanoff, and Barton have their first solid lead on Barnes for Rogers and Wilson after a week of combing through data. Rogers and Wilson hop on a plane in short order with no indication of when they'll return, but Tony is sure they will.
And, just in case, he makes sure there's another apartment ready for when they get back.