18 players registered so far, squad of 23/24 means at least 5/6 more signings, maybe more if Brown and/or Cassidy leave.
2 centre-backs (Hughes and Burgess based on rumours), at least one centre mid, winger (Ideally needs to be quick, so we can strech teams similar to how Forte would) and striker (Baxter?).
I'd say thats the minimum needed. Then look at getting another option at LB and someone who can play across the midfield. Possibly a 5th striker later in the window if the budget will allow.