AFAIK there isn't a Roshi's Island that uses a 'MysticSSJ4Goku.wad'. Did a friend make the map and send it to you? It's kind of a popular 'first map' to make.
As for making a map with Dragonballs, make a map in Hammer and put 7 or more 'item_dragonball' entities around. Just make sure they're not touching each other or any of the map brushes *cough*esf_riverside*cough*.