On lvl3 you should be able to win league with avg. 4 stars first eleven, of course check other teams and their ratings. Use your best players for cup and champions league unless you have 2 strong opponents in one day, then use green packs...
I suggest you to get players for every position if it's possible, then you'll be able to use all possible formations, that's sometime more important than quallity.
My team lacks only dmr to cover all positions.