Yes, it will fit (it's the same one I linked to) and the Reedy will be faster than your P2K - how much depends on gearing (yeah, I know - he' talking about gearing again - doesn't he ever quit that?) but the truth is the gearing for every motor will be a little different to get the best out of it. I own on-road (TC3) so I don't have experience with the T4 directly but I saw that someone else answered that in one of the other threads on this same subject. (Have you tried re-gearing yet? - it'll only cost you a couple of buck to try it out.)

As far as what you need and maintenance here, again, is something copied from earlier in this thread. A can of motor spray is about $5 and should last you quite a while - spray out the motor every couple of runs in the dusty conditions that a buggy usually sees and keep it lubed. Don't get oil on the comm where the brushes contact or it will arc - just a tiny drop at each end bearing after you spray it out - too much oil will just give the dirt something to stick to. Your LHS can also go over all of this with you in person (if they will - as another thread notes customer service varies greatly from store to store - I'm lucky in that the guys at my shop are quite helpful - I hope you have the same luck. This stuff is much easier face to face than over a forum.

If it's real speed you want you'd be better to start saving money toward a brushless system. They are initially expensive but there is very little maintenance and they really fly compared to a 27 or a 19 turn. Try using the search function to look for brushless threads here - it's been discussed extensively. Be aware that the faster it goes the faster it will suck up your batteries.