I'd rather we were using Scott Smith at left-back to be honest. He was decent enough at centre-half last season when required to play there, but I'd feel more comfortable having a natural central defender partnering Andy Graham and utilising Smith's abilities as a full-back. McNiff and Smith could then act as cover for the first choice centre-halves if necessary during the course of the season. We've got three players who can play left-back (Smith, Linton, McNiff), three who can play right-back (McGinn, Graham, Horne) and three who can play centre-back (Graham, Smith, McNiff), so a natural (right footed preferably as Smith and McNiff are lefties) central defender would complete the defence for me.
Phinn's definitely for ability and if he comes through pre-season without anymore injuries then I'd be comfortable with him signing up for the season.
In an ideal world I'd be looking at us to add another centre forward as well as another centre back, so hopefully we can get Kevin Smith signed up as well as a defender. We'll almost certainly run with a smallish squad again, so if we got those two plus Phinn signed I'd be happy with that squad going into the new campaign.