It is large enough for 1.1 but just barely. I would remove the buck when the female has a litter, because it will be very crowded. I run my mice in lab bins, and I keep 1 female in a lab bin and move the males around when i need them, but remove when there is a litter on the way.

It will not stress out the male to be alone, or with 1 female.
You can sometimes find KKs at yard sales of flea markets pretty cheap, also check reptile stores for used ones, I get the large ones all the time, for like $3 used at the reptile store here.