NPC's wouldn't be too difficult...Storyline however is where it'd get complicated, being that there isn't much to Dragonball, besides fight fight fight, and try to get your wishes granted via the namesake.
It was intense. They blew up the world when his Super Dragon Punch or whatever, when the golden ki dragon wraps around his hand, collided with Superman's Mass Infinite Punch. Goku lost sadly. And I would gladly pull it off if you helped. I can't say I've ever GM'd before.
Gohan never does become an actual Super Saiyan 3 or 4. In the Super Buu Saga he becomes Mystic Gohan, which is pretty much equivalent to SSJ 3 1/2. But Goku becomes SSJ3 in the Fat Buu Saga, then 4 in the Baby Saga of GT.
I'd totally join one! So long as it's DB or DBZ, unfortunatly can't say I'm too much of a fan to the GT Serise even though I've got the whole thing. Only part I actually enjoy is the Movie with Goku Jr.