Junior had polio as a kid, which is why his leg looks kind of weird. He doesn't toprock much, either.
He's a little bit lighter than most bboys his size, but there are guys (Kujo, Darkness and Cico come to mind) that can do similar moves.
Here's a vid with Kujo for comparison;
Also, having dabbled with this type of thing in the past, I would say that lifting weights is strictly ancillary if you're trying to achieve a planche or a flare. It requires a large degree of strength from awkward positions and body awareness, not to mention familiarity with basic gymnastic moves.
Things that would probably be most useful for bboying would be;
*"Baby" or half-planches (at least to start, 'cause planches are fucking hard)
*Handstand pushups (this is a big one. The more strength you develop here the better)
*Handsprings, cartwheels, etc.