I would always aim for a minimum benchmark of a 5* first XI in the earlier levels, when you get to about L8 or above, then its time to get 5* subs as well and even have some players that are 6* in your first XI, this will ensure you are competitive in the league and champions league each and every season, you may not win it every season depending on your opponents but it should get you close to winning at the very least.

As you move up through the levels the relative quality increases slightly and general activity of rival teams also increases slightly.