First of all you cant be majin buu or goten or vegeto or bardock or gogeta with out a game shark.
(can't be bardock at all) Next, the easy way to get all the dragon balls is to get 8000 zenie and then go to mr popos shop.
Look at recommended and if it doesnt cost 8000 zenie exit and re enter. Keep doing this until you can find a dragon ball.
Might take a while.
For advanced players that can beat advandced story mode easily then keep beating it. it gives you a dragon ball every time you beat it.
To get players:
Hercule: Beat Adept in world tourny and buy him from popos shop.
Great sayaman:Beat advandced world tourny and buy him.
The rest you get in story mode.
Also, in tourny mode try to knock them out of the ring, it gos alot faster.
To use dragonballs go to edit skillz and then to skill list. Go over to dragonballs and press x then x agin. Select yes and it will show a vid of summoning the dragon.
You can pick to have all skillz for one person. it only lets you pick out of 3 characters.You have to equip this at the change caps menu.
Hope this helps.