Good post, I think I posted something like that in another forum a year or two ago, and it's something everyone talks about when evaluating Bargnani (I realize this post is not about him). Talking purely from a traditional sense of positions and what each position brings or is SUPPOSED TO bring, you can't count Bargnani as a starter. Even though he is, and will always be one on this team.
By my estimation we need the following starters: G/F, PF, C. JV, I guess, could be the future C. But then again 5 years ago we thought we had drafted our future starting C for years to come and then he was moved to PF and still isn't the prototypical guy you need there. But I guess I can concede that position to him for now until we know more.
So really we need SG/SF, PF. This, mind you, is for NBA starting caliber. If we're talking about a team that might make the playoffs and go past the first round, then we need starters for all positions.