Everything listed up there afects possession..I don't know the exact numbers but i've noticed that playing against 1-2* lower team gives you possession boost..
1 thing is sure, possession is not only afected by midfielders.. a while ago more ppl in midfielder position would give you more possession, aparentlly they've changed it now..
Red card should be 5% possesion penalty or smth like that.
The best way to get more possession is:watch ur games, get supporters to watch yours.. u'll have 15% boost and u'll see 60:40 most of the time.