How do you define "strong"? Are you doing any weight training right now?
It's going to be harder to build muscle with all that activity, but it's possible. Take a look around the Combat Sports forum, specifically the "How to Train" thread:
You might find some more useful training info there. But based on your 12 hour training commitment, I'd probably consider something high intensity, low volume.
Presuming there's no way to cut back on your capoeira, that would be the best compromise between limiting any further activity and stimulating some muscle growth.
But like Popular said, a lot of your progress is going to depend on how you eat ... um ... are the stats in your profile correct... "6'5", 180 pounds, and 26% bodyfat"??
Dude, talk about starting with one foot in a hole. You've got a lot of ground to cover. (By the way, how'd you calculate your bodyfat?)
Read through these three articles to get an idea of how to plan your nutrition:
Also, you should try to have one or two protein/carb shakes during your crazy-long capoeira training. That will help to prevent burning any crucial calories.
Why? A weighted vest won't do much of anything in terms of helping to build larger muscles, which is what you said your goal is.
That said, Ross Enamait (a top notch boxing S&C coach) often uses them as part of a conditioning program, as do some powerlifters, though I still don't think it's necessary for your situation.