I don't own an 808, but I'll do my best to answer some of your questions.
With the RC-Monster conversion, pinion gears are used. These are the best available on the market at the moment in my opinion:
http://www.rc-monster.com/proddetail...=5mmmod1pinion
The Tekin RX8 just came out and seems to be doing very well for most people. It is designed with racing in mind, so it will probably work for you the best. Just choose the KV depending on what voltage battery you run.
http://www.rc-monster.com/proddetail...=tekinrx8combo
The ESC will do perfectly fine without mechanical brakes. There really isn't a best place to put the ESC and battery. I mounted my battery/ESC like this to give you an idea:
http://s199.photobucket.com/albums/a...t=IMG_1104.jpg