3 or 4 defenders is fine! its your choice!, However your formations I dont use I do this way 3-1-4-2 or 4-1-3-2.
DL,DC,DR,DMC,ML,MC,MC,MR,ST,ST OR DL,DC,DC,DR,DMC,ML,MC,MR,ST,ST, this has served me well over the last 6 seasons, if you want anymore help to play these formations just pm me.