I have run a P5 in my buggy and truggy for 2 years. Never had a problem with speed or power on ANY track. It is the best engine out for the money. If your actually racing, speed will not be a concern on 98% of tracks. If you cant control the car, not matter what engine you have you will not do good. You do not need a modded engine. Coming from Drag to off road RC two different things, you will need to learn to drive.
Tools, I have a set of Arrowmax, Losi, a few Hudy ----- the best tools Ive owned was Dynamite machined hex wrenches. They are also the cheapest tools Ive brought.
My Savox 1268 servos, have been awesome. There are plenty of good brands out there.
I carry alot of stuff with me to each race, you should get to the track see what guys have. You dont need everything I take...
There is ALOT of good information on here. Even at the track, there are guys newer than you that could give not great advice.