A natural RB should be an absolute must. Gilchrist and Shackleton are both fine options, but neither of them are pure fullbacks. Having someone who can always be relied on, akin to how we had Baldock/Bogle last year, is a must for me.
After that we need another striker. Moore looked very good on Friday, but we cannot go on assuming he'll be available for every game. Having someone of a similar type, who can play that link-up role with the attacking mids, would be highly valuable to this squad.
I'd also want a natural LW. A right footer with pace who can do that role of cutting inside or out, depending on the situation. It would free up the likes of Hamer and O'Hare to play either as a CAM or DM, as they are both far more effective playing centrally.
I noticed a few votes for a DM, and I wouldn't be opposed to getting an enforcer-type player in as a Souza backup. But I don't think it's essential. If we make signings in the above positions, we'd have Hamer/Souza/Arblaster competing for starting positions at DM, plus the likes of Tom Davies & Shackleton (when fit), Peck, and perhaps Coulibaly if we don't sell him. Not an area I'm too worried about.