Depends a bit on his formation. He has played 433 with the point forward and backward. If it's backward (like we currently use) the 6 is important for the buildup and the passing range will be very important.
If the point is forward the 10 is more important, and the 6 will have less of an influence. Overall it's an important part though, and it surely will be one of his criteria.
OT: I'm not sure if Gundogan is a player we need right now. Van Gaal said he bought Blind for midfield, if we already buy a replacement for Carrick, while he's still here, what would that mean for Blind? He's defensively aware, reads the game well and has a great pass in him. He's done well in his first season, he looks like the replacement for Carrick to me.
I think we could better look for a backup for Herrera who could play 6 if both Carrick and Blind are out, while still maintaining the defensive balance. Otherwise we'd still see Rooney in midfield next year since Gundogan isn't very good defensively. If we buy Gundogan we'd still need another midfielder, since we're short on defensive midfield options.