These are some self inserts about ideas of what to do with each clan. The hardest part is really trying to make them keep up with Naruto and Sasuke. as well as the other S-ranks.
SI 1: Yamanaka Clan
Maybe some type of self insert into Ino or a cousin. OC would be a sensor, as well as fight similar to Kabuto with chakra scalpels and can also heal themselves. Also, an expert in clan techniques as well as genjutsu. The OC creates a combination of their clan technique and genjutsu, creating an unbreakable genjutsu of some sort. If you combined a mind walk with a genjutsu Im sure you could bullshit logic your way to getting something unbreakable. Make it mad chakra intensive though. To balance OC's genjutsu abilities out, ninjutsu should be light and supplemental at best. Stuff like Hiding in Surface Technique.
SI 2: Akimichi Clan
Alright not enough people put respect on the Akimichi name in my opinion. Has no one seen Attack on Titan? They already have large chakra reserves. Especially with calorie control. Use their partial expansion technique on shuriken and kunai - even that alone is a ridiculous ability. Use their partial expansion to throw rubble like the beast titan. The whole idea of calorie control is to convert fat to chakra. What about its inverse? The ability to take someone else's chakra and turn it into fat. It should only work with pure chakra, so you'd have to bite someone for it work. No just eating ninjutsu lol. The OC can still become a ridiculous tank then. Give them the five elements and do some cooperation ninjutsu too.
SI 3: Nara Clan
Naras are hard because their minds are meant to make up for a lack in combat ability. One idea though is an actual "shadow clone". This clone made of shadows should be able to burst on command - when they do anything caught in the radius is paralyzed. This could be more of a summoning, so it's more limited in its use - like a Nine Masked Beasts of Valor type of technique. Maybe there's a reform period of a day for each of these beasts after they burst to balance it out.
SI 4: Aburame
Like the Akimichi, the Aburame don't get enough respect. The applications of their insects are wide. Consider shurikenjutsu - by placing some insects on their weapons, they could remote control them. Imagine three or four insects on the handle of a kunai or the finger hole of a shuriken. Insects have an incredible mass to strength ratio, so this should be feasible too. Also consider how their insects can suck chakra - can they inject it as well? Injecting chakra can lead to Genjutsu usage and application that is extremely subtle. Who would notice a few insects on them. Then also consider injecting chakra with a change in nature. Could be extremely painful. Lightning could cause nerve damage, fire could cause internal burn damage, earth could cause hardening of tissue. A lot of room for different things here. Aburame do have lower reserves so giving the OC some type of medical ninjutsu is also on the table. Slap them with a summoning contract too and it should be good.
SI 5: Inuzuka Clan
Inuzuka seem to be average for their chakra reserves, but they do have an emphasis on taijutsu. Average chakra reserves also means the ability to do ninjutsu as well as Genjutsu. Some type of auditory wolf cry Genjutsu as well as some use of basic elemental ninjutsu could work well. You could combine the rotating fang with lightning release to increase Piercing power. While this might not seem like a lot to get them pretty strong, the strength of the Inuzuka is the fact that they're working with a dog and their cooperation with their ninken. Trying to load them with a broken ability won't mesh well considering they have average reserves. But, the cooperation with the ninken can be extended. Considering that the ninken can transform into a human and use hand signs and ninjutsu, what about elemental cooperation techniques? Is there a limit to what the ninken can cast? Is Genjutsu possible? If you look at this, you could assess a sole Inuzuka's abilities as a two man squad. Teamwork can greatly increase attack power. Hell, give an Inuzuka four dogs and you can have five elemtental releases.
SI 6: Hyuga
The Hyuga have the ability to see for kilometers. Give them archery! Slap some lightning release on their, and it should be a strong ability. To further buff their close range abilities, you could take advantage of their ability to release chakra from all of their tenketsu. Let them produce a blast of fire from each of their tenketsu to aid in movement and speed. Like a fire version of the lightning armor. The Hyuga can see chakra, so medical ninjutsu seems like a good place to go as well.