General Tactics
The main reason you'd want to play Vegeta in DBFZ is his Assist. This thing is stupid good and it does everything you could ever want or need. His assist will pretty much synergise with anybody, given the sheer, unadulterated versatility it brings to the table. As such, you don't really need to build a team around him.
Team positioning
Point
Not Recommended. While Vegeta can serve as a point, it's a massive waste given the sheer power and versatility of his assist.
Mid
Vegeta is always doing good as long as he's not point. Between his amazing assist's power to extend combos, secure blockstrings and flexibility, Vegeta will always be useful.
Anchor
Same as Mid. Put Vegeta in the position that suits your team composition better.
Picking Teammates
Literally pick whoever you want. He's THAT versatile, and being a big softy at heart means that he'll always fit in any team, as long as everyone's in a good position.