I usually buy one or two players via offers. 2-3 has been enough so far. I look at playrrs in leagues above me on the first day of the season, and if they have 5 star near 99% players under 21, that arent in their first team (so its a 3-4 star for them).

That way they can buy one or two 5 star players for subs, and i get a great player for my level. My offers are smartly placed, and so almost always accepted up to now.