The plow requires traction (weight), the bushhog requires HP.
The CK27 is a rather heavy tractor for its power.
According to the PTO HP, a 4' cutter would be perfect, but wont cover your tracks. So I'd get a 5', you pay just have to slow down in places.
As to the plow, you have a pretty heafty tractor. It will probabally pull a large sincle bottom, like a 16", or two smaller bottom plows, like a 10 or 12.
I'll let other who actually have a ck27 chime in now.