Theoretically, the Leafs could protect 8 skaters and 1 goalie. The big 4 forwards and our top 4 D would likely be protected. This leaves Kerfoot and Dermott as the likely players Seattle takes.
And as csick said above, Dermott is the likely candidate heading to Seatlle.
I believe it is 60.2M. If you click the Cap Friendly sign on the top left, then scroll down to 2020-2021 cap space, it says upper limit: 81.5M, lower limit: 60.2M.