Yes, the Hyuuga clan has the Byakugan, so your character would have to be a member of the Hyuuga clan. 

Combat style is more like how do they fight, do they run straight at their opponent? Long range attacker or short range attacker? 

Nature releases are Fire, Water, Wind, Earth and Lifhtning. Some of them are strictly used with special clans. Fire is weak to water, Lightening is weak to Earth, Earth is week to Water. I'm not sure about Wind.

S-Rank is like top knotch but takes a lot of chakra. A-Rank is not as good as S-rank but takes less chakra and B-Rank is pretty good and takes less chakra than both S and A rank. Pretty much Jounin and Chuunin have these ranks for Jutsu. 

Anything below those ranks like C, D, E and F ranks are pretty much week and anyone can do, Genin Level Jutsu. 

Prince has a form to make your own Jutsu, he said at most six Jutsu unless you have special permission.