SI: Average guy
I always thought it'd be interesting to consider an average person with completely average stats. Average chakra control, average chakra reserves, average talent, etc. Then tragedy strikes and they have some type of new drive to improve. A lot of the first part of the story can be focused on trying to improve basic skills like taijutsu. The chakra affinity can be made to be whatever is most common in the area. Also, Jutsu should be hard to come by. Rarely anyone should be handing the OC a ninjutsu or Genjutsu, unless going though some type of basic training. The OC can start out in Genin corps without a jonin Sensei, move up to a chunin squad, and then go into Anbu, and then jonin or something. Most of the time they should be having to pull themselves up without any help. As for abilities, the OC isn't being handed Jutsu so elemental release should be confined to chakra flow for a good amount of time. Then it could be a single Jutsu - like chidori - which then has many variations - like all of Sasuke's variations of chidori. Or, you could go a different route and make a new ninjutsu without elemental release - like a lead version of Konan.
SI: Kankuro
Being a puppeteer is pretty interesting. One puppet idea is Raijin, which looks like the Japanese deity that has control of lightning. Consider a four armed mannequin with hammers in each hand and an oni face. Put a hammer in each hand. In each hammer put an electromagnet so when the hammer spins you generate a current (kind of like Thor). Add some chakra bullshit logic and spinning the hammer can augment blows with some nasty lightning. The deity Raijin has drums in a ring around him. You could put special sealing formulas on those drums so that when they're struck something happens. You can then consider allowing it to throw the hammers as well. Another puppet idea is Fujin, which looks like the Japanese deity of wind. Those bags of wind can be replicated as chakra enhanced air guns that can release a great big bust of wind. This puppet could be used in tandem with Raijin to form a pretty deadly duo. Fujin could keep people away from the user and Raijin could be the attack force. Another route for power with the puppets is go the human puppet route, but focus less on kekkei Genkai and more on senjutsu. If you could combine cursed seals with the puppets there's a lot of potential there.
SI: Rock Lee
Ok first off, Rock Lee needs a weapon. That's honestly up to the writer - I prefer the three sectioned staff. Next, Rock Lee can do a lot more without chakra than he does. He could look into poisons. Using poison can make him a much stronger opponent and open up long range attacks for him. Next, Rock Lee can use ninjutsu. Not in the conventional sense, but he can walk on water. This means he can channel chakra. This means he can use paper bombs and other Jutsu shiki.
As a quick aside, I assume that Jutsu shiki is the art of using special ink to write down a select few characters on some special paper such that, when chakra is channeled through it, some result is achieved. Fuinjutsu is the art of sealing one object inside of another. Because sealing is such a complicated art, it's often easier to use Jutsu shiki as a medium for fuinjutsu techniques. A note on chakra printing: chakra printing is the set of techniques to use chakra in forming Jutsu shiki instead of ink. In my eyes, the hand seals for the summoning technique just aid in chakra printing the formula on the ground. The blood is placed o the Jutsu shiki and when enough chakra is pumped through it, the technique summons a creature.
Back to Rock Lee, he should be able to use Jutsu shiki because he's capable of chakra flow. That opens up the whole world of traps for him as well. So super speed, traps, and poison - he could be another Hanzo of the Salamander. By carrying around the Jutsu shiki for the summoning technique already, he can also summon - a Komodo dragon would be cool. It would give him a special poison and possibly a fire Jutsu. Note that Rock Lee really is one of the best people to give Jutsu shiki to. Chakra printing can make this ability ridiculously op - Rock Lee's shortcomings elsewhere balance it out well. If you do want to make him broken, you can make a self healing Jutsu shiki that should automatically use Rock Lee's chakra to heal him - would work amazingly with the gates.