What's a way I can play through every gen again but I catch and use every Pokemon/add restrictions to make the games actually hard?

I used to take on every gym with new Pokemon each time, with the same number of mons as the gym leaders themselves (no items). This was fun, challenging at times (especially at the champion, but I could use any Pokemon at the League). However I want a way where I can catch them all, and use them all. Or at least make things harder.