I am kind of torn on who I think will start. I guess it can go several ways.
Short and fast:
Fox
Monk
Briscoe
Willis
Adebayo
This line up has 3 guards that are 6'3" - 6'4" and 2 post players that are 6'9". I call Willis a post player. But, in reality, he is a stretch 4. Would be fun to watch these 5 get out and run. Then have Gabriel, Humphries, and SKJ as the bench. No real backups at Guard. But Cal can rotate Gabriel and Willis to the 3 to rest a guard.
More Conventional:
Fox
Monk
Willis
Adebayo
Humphries
This is a more conventional with two guards, wing forward, power forward, and Center. This line up would be slower, but have better size. Have Briscoe as depth at guard and Gabriel and SKJ at forward and center.
I am certain Cal will switch things up throughout the season depending on who is hot and the matchups. Either way, it looks like it will be 7 or 8 player rotation.