You are right, you aren't going to get much for them. Two things to take into account, what is the quality of the players and how old are they? For example, if it's a 30 year old with 80% quality, he is still worth keeping. However, if it's a player with less than 75%, then I would try and sell and get whatever I can for him.

In terms of squadsize. I have a large squad depth of 22/24 players. I enjoy having a large squad size because there's so many positives that can benefit your squad, plus you save on using rest packs because you don't need to keep using them to boost the players energy back up.