Read your posts and I have some input for you. I have converted a Kyosho K3, Ofna Hyper 7 and Hyper 8, and a Mayhem. So I do have a little experience. I have tested the following motors and controllers:
Novak Hv system
Shultze controllers (several including uforce and 18.149)
Bk controller and motor
So as you can see I have a broad range to base my suggestions off of.
First off, Metal spurs are not the best choice as you heard they eat pinions. Try to use a kyosho or Ofna diff and retro fit it to your car and then use a kyosho plastic spur gear(will fit on both diffs) part# IF148 available at Kyosho America if you call them. I personally like to convert either a hyper or a Kyosho so that it makes things easier with this step, but if you are set on converting another, you will just have to do some mod's. The other choice is to get a hardened pinion, which I have not personally tried, but I hear it will last a while. Plastic spur's last a long time if gear mesh is proper and they cost around $7US, so very reasonable.
Second, I would definatley recommed Lipo's, don't even bother with the nihm, unless you just want to Bash around in your yard. Here is a link to a place that has awesome deals on lipo's and they help to make it a little more affordable. http://www.maxamps.com/index.html?lmd=38743.678854
Order 2 2s2p 6000mah packs and wire them in series to give you a 4s4p pack. This is the proper voltage to run with an 1/8 scale buggy. It will be plenty of power and should get you close to 15min's of run time.
Next, the power system.... This is a little more complexed. I read where you are trying to figure what kv to get. Pesonally I like torque for 1/8 buggies, I have tried rpm motors and I just don't like them. This has more to do with the poles of the motor than the kv though. It is good to understand about kv, but it is more about what works in the real world, not on paper. Kv will get you in the ballpark if you understand it, but it doesn't always get you the best motor. That is why I like to try what others are saying work well. If you want to tell me what you plan on doing with it, I can better give you a suggestion. Are you going to race it at a track against nitro's or are you just planning on bashing around your yard with it?