From all accounts, Mag was one of our top targets in the portal. I don't think KY beat out SDSU, Clemson, USC for Mag just so he could be an end of the bench, hyper situational player, and I don't think Mag would have come here to play that role either. I agree that Mag could create some spacing issues, but the guy has shot the 3 at a decent clip in the past. My guess is KY plans to maintain Mag's attempts but much improve his efficiency.
Also, we know Mag factors into the plan because KY went and got him. All the guys already on roster were inherited, it would make a lot more sense for them to be fighting to find a place in the scheme. Like Fous for example. I love Fous, but there's at least 3-4 guys we'd rather have with the ball in their hands. It makes a lot more sense to play Fous coming off the bench, bullying opponent's backup 5s on the block without clogging up the primary offense and taking fewer touches from Demin, Hall, Baker, Catchings, etc.
So, in response to your guesses, here are mine:
Hall won't play 30 minutes. Unlike last season, we have the luxury of depth and Demin will be leading the offense a lot anyway. We're not redlining Hall all year.
Demin and Catchings are each going to play a little more than 20 minutes a night. They'll play similar minutes to Hall and Saunders.
Knell will have a big role, but not a 20 min a game kind of role. Maybe some nights, but I'm guessing he averages 10-15 min for the season.
Koz is going to be good, but it won't be this year. I'd be surprised if he averages more than a few minutes a night.
Saunders, fewer minutes. My guess, he averages something in the low to mid 20s to help maintain his high energy, glue guy role.
Mag gets at least 15 a game coming off the bench (although there may be games he starts over Saunders for matchup reasons).
Keba and Fous will play similar minutes, if anything Keba will be the one coming out on top of a 25/15 min split. Keba starts.