Consider that half will be away at any given time, and then they may or may not be great. Having a couple extra isn't a huge issue because every conference has a fairly heavy streaming or pay network portion.

But with byes and bad matchups, I think I'd lean 6 (in a larger conference). 4 also does work, but you'll definitely have moments where 2 are away, one is on bye and you're left with 2-8 Kansas @ 1-9 Arizona. More importantly, with four teams and two evening slots each week (one on ESPN+ and one on FOX/ESPN) that means that every one of your Western teams only plays evening home games

8 means you're more likely to have a good matchup but it's probably unnecessary overkill.

So 6 would be ideal, but anywhere from 4-8 is a workable amount in my mind