As emu26 pointed out, as well as riderczech's on the P9 thread, the bb is ridiculously low. With 2.8's and 30% sag I hit stuff so only expect the problem to be worse with 2.4's, some guys even use 165 cranks to get a bit more clearance, now as to rideability I'd say it's probably not worth it since you'll be more worried to not get pedal strikes than having fun.
About the fork in the P8 I'm not sure how low it's bb is and the 150mm would rise the frame yes, but the P8 is designed for a fork having 100mm if I recall correctly, that means using a 150mm is possible but conferring your safety to using a frame out of its design specs is not the greatest, it can happen that the front part of top of the frame gets ripped apart in a landing.
As for the size I'm not really sure, you should measure your bike and have a look at the dimensions for the frame you choose.
If you want my opinion I'd say buy the frame, sell the bike you have and use the money to get the parts you want, bear in mind that with this bike it would be either a 27.5+ or a 29 build. I think my p9 was a great buy, the only issue are the pedal strikes but we get stability/antisquat/progression so like everything is a compromise, here's a link to the linkage review of the norco range which you'll notice looks awfully similar (if you want to see for yourself ICAN uploaded the P8 and P9 models for the linkage simulation):