jimmysisson, the manufacturer recommends 25Kw or 33 hp. It stalled my 39hp 3011 so i geared the PTO speed down to 400rpm through the main gearbox (putting the range lever in neutral) then it broke my PTO shaft U-joint yoke.

when feeding an 8" oak in the hole, the shearbolts on the main drive sprocket breaks.
At 540 rpm i run the tractor at 1400-1500rpm which gives enough time to feed the log or beam into the hole. My 55hp tractors both run it like its a baler: hmm-hmmmm-hmmm.
when cutting 3 by 8" roof beams of the ban were tearing down, it maintains a pretty constant rpm.
I would say, expect 55hp and this machine, to do 6" oak without abusing either the tractor or the machine.
About blade sharpening, they are Hardox 400 blades like used for earthmoving cutting edges.. I cut scrapwood with nails all saturday long, about 12 m3. With a chainsaw you can do 5m3 of clean firewood before you need sharpening, so when not cutting nails, the blades dont need sharpening every year.
You do have to adjust the blade clearance properly, to reduce the recoil of the wood, which gets kicked up a bit. With long logs you dont notice it, with short logs you must allow the machine to pick the wood up from your hand, not trying to hold it or it pushes your hand between the wood and the safety shield.