In a perfect world you don't want "squad players." You want 20 outfield players who could all start and you wouldn't feel your heart sink if they did.
In an ideal world being the key mate. You cant have 20 players of the highest calibre in the team. Well at City and PSG probably. But not at the genuinely managed clubs. The premier league has allowed 23 players to be declared as the PL squad.
McCarthy, Schneiderlin, Vlasic, Baningime, Dowell, Besic, Bolasie, Niasse, Tosun, Mirallas, Sandro, Tarashaj
Possibly Walcott
3 GKs. Pickford, Stekelenburg and Hewelt/Virginia. We are good here.
Out of the remaining 20 players, lets split into 8 defenders, 6 midfielders and 6 strikers.
Coleman, Keane, Zouma, Digne - Main defenders.
Baines, Jagielka, Mina, Kenny - Backups
But we need atleast 1 CB here that can complement Jagielka and fight for that spot. Then we will have 3 CBs fighting for 2 spots. And if we are to sell Jagielka, Baines and Pennington, then we WILL be a lot short. We dont want to over rely on our youths for a starting spot in the premier league.
Gueye, Sigurdsson, Bernard, Gomes - Main midfielders
Schneiderlin, Davies - Backup
We are a whole lot short here and we HAVE to invest in an ball playing CM that will allow Sigurdsson to push forward.
Strikers we need atleast 3. Two wingers and a striker if everyone off your list has to leave. But thats not going to happen. We cant sell first team players and rely on 16 year olds as backups to compete in the league. We will need a 32/33 year old striker who will be happy off the bench and a couple of understudies to him and DCL.
On wages front, assuming these 20 players have an average wage of 100k, thats 2m a week of wages freed.
We would need a CB, a FB, a CM, 2 Strikers and a winger irrespective of the players leaving to even complete the first team XI. I doubt we (or anyone in the history of football) are dumb enough to sign off 20 players and have only 6 players sign in.