I have 20 players. I try to have 14 players that are interchangeable in starting 11 without noticing any difference. The others play now and again but usually just cover for suspensions or subs to keep condition up on players I want to play again. And they're usually ex-1st team or panic buys..

My core 14 players usually comprises players for 4-5-1V + ST, MC and DC/X - although its developed that way rather than being some grand plan.