1) Yes, it's a great idea to divide teams not by level, but by league as in associations. It will be more like real football. And make a decrease in quality when moving to a new league, and not from increasing the level. Level would affect something else, not quality. But that's another game. And I would suggest out of 16 teams 8 raise, 5 the same level, 3 relegation.
2) I don't see any point in tanking, why are managers doing this?
3) Lost in translation, I don't understand what you mean.You cannot buy players below 40%.
4) In real football, Barcelona always plays with Real Madrid. You wanted realism or boring?
5) I score 100+ goals every season. The problem at the initial levels is not in the engine, but in inactive managers and "dead" teams.