Main priorities for me are a CB, AM, winger and a back-up striker. AM, winger and a striker could potentially be covered by 2 signings though.
I think we need to pick up a guy at his peak or close to at CB to bridge the gap between youngsters like Holgate and our senior pros in Jags and Williams. We're almost certainly going to need a new, young LB, with Garbutt seemingly not rated and Baines getting on. I think if we can get our hands on a top class keeper it could be worth persuing, but the don't think the position is a priority considering how Robles seems to be developing.
On the flip side l think we could go without a new RB, since I don't mind Holgate, Kenny, Connolly, etc picking up minutes in the cups or if Coleman gets injured. Holgate especially really impressed me when given chances there earlier in the season.
I'm not particularly knowledgable when it comes to up and coming players, but some of these guys would be on my wish list:
GK: Hart, Butland (if fit)
CB: Koulibaly, Manolas, van Dijk, Keane
LB: Robertson, Davies, Rodriguez (he's basically the new Baines anyway )
AM: Sigurdsson, Lanzini
Winger: No one really coming to mind. Maybe a Redmond or Zaha.
Striker: I wanted Perez or Gabbiadini over the summer and Perez especially would arguably be available and cheaper now. Could be interesting to see Rooney return at the right price too.