MLB expanded to 36 teams. Fictional players. 3 divisions of 6 teams, no interleague play.
Schedule favours divisional play. 18 games vs div teams, 6 games vs teams in other 2 div's.
3 div winners plus 1 WC per league. Top 2 seeds get 5 home games in first round of play-offs 2H, 2A, 3H.
Rest of playoffs 2H - 3A - 2H.
I have some settings that may not necessarily be realistic, such as levelling the financial field and market sizes a bit, making sure owners are in it to win and not just profit. But then that's the beauty of OOTP, you can do things that aren't realistic and still enjoy the game of baseball very much.
Create your world and live in it