Get some protein and carbs in there and lif weights to help build mass. Keep in mind that it is possible that you will lose some of the flexibility while gaining mass. Your cardio will definitely be affected if you do not keep up with it while bulking up.
As for the fighting style, it is really what you want to do. You are long and flexible so I think you would do well in BJJ. But wrestling, judo, or other disciplines would work great as well. Same for striking. Whatever you are interested in and will work hard and stick to, is what suits you the best.
Sig Credit: M.C
Miesha Tate - Urijah Faber - Dustin Poirier - Frankie Edgar - Claudia Gadelha - Tecia Torres - Demian Maia - Jessica Eye - Diaz Bro's