re: Any early guesses on who will play right away?

Depends on how we want to use the slot. Mizzou has tried to have the best receiver in the slot historically. Players like JMAC, DA, Coffman, Egnew, & Lucas have excelled there. If we want a big receiver there it's probably Brown.
I picture JJ in Murphy type role. Line him up everywhere. Floyd could also fit that type of role.