I always work on the basis that you need at least two players for each position - three if you play with one striker
I would bet good money that we see the following players leave either in January or at the end of the season:
Howard
Hibbert
Osman
Pienaar
McGeady
Oviedo
That would leave you with the following as proper first team options:
GK: Robles
RB: Coleman
LB: Baines, Garbutt
CB: Stones, Jagielka, Funes Mori, Galloway
CM: Barry, McCarthy, Gibson, Besic
AM: Barkley, Cleverley, Naismith
RM: Deulofeu, Lennon
LM: Mirallas
ST: Lukaku, Kone
Granted, a couple of those players can pay in more than one position, but assuming I'm right about the players who will end up leaving (and 4 of those 6 are out of contract), that leaves you with goalkeeper, right back, left mid and striker as the priority areas.