Kyosho spur fits fine. Also, the pinion size will be depending on your setup. I run a 2000kv 1512 2.5d in my CRT and find my pinion choice to be around 15t. I'm only running 4s though. If worst comes to worst, you can run the LSP ring and pinions to give you more gear.
Also, if you haven't ordered your motor mount yet, I suggest ordering the car mount. Combine it with the diff posts from the car. You will have a much lower center of gravity this way. The motor slots will also be in a better location allowing you to use a fuller range of gears. I've never tried it, but I don't think the smaller pinions will fit on my setup (I accidently got the truck mount).
I will be using 4s most of the time and i would like to have as tall of gearing as temps will allow. I found a 50T HB Lightning spur that might work.
I'm telling ya, I don't think it will be fast enough for you. Plug it into Brian G's speed calculator. I don't remember the results when I did, but it seems like my truck is pushing 35 with the tall gearing I have. Again, I'm running 46/15.
What kv of your motor you said 4s whats your tire size. have you punched it into speed calculator remeber crt is geared same as buggy
I punched in with a 2000kv rateing and 5.6" tires its says approx speed of 55mph