IMHO the main priority has to be at at the back. At the minute we've got Diamond, Considine and Mulgrew all three of them under 23. Then we have guys like Crawford and Stirling Smith and Rogvi Holm who, at 19/20, should be looking like they are beginning to push for a place in the team squad. Add in to the equation no decent backup for Langfield...
All that adds up to a defence screaming out for an established, steady, experienced, head to help these guys develop.
In the middle with Duff, McDonald and Kerr we at least have some older heads to help the likes of Aluko, Pawlett (and again I think Stewart should be making a claim for a first team place this season). I suppose another established player would add strength in depth and take the pressure off the younger lads and perhaps the defence.
Up front with options including Mackie, Wright, Miller, Aluko and Paton, I can only see this being one out one in. Fingers crossed it's Wright.
All in all, given that they would need fuck all time to settle in, McGhee knows exactly what they can do, and they know the Scottish game Smith, Kimpl and Hughes sound like ideal candidates??