Cool.
You will love it brushless!
your q's;
(depending on the amount of cells you want to put it thru..)
1>Neu 1512 or 1515, or a wanderer 8-9XL
2>Quark 125
3>Yes, Mike. He can machine you one, but from stock L profile or a sheet, you should be capable of making one youself. WIth a dril, dremel, rasps and most important, some patience you can do it yourself.
Get a Kyosho 46T spur from Mike, and he can help you with the pinions as well. Your LSP has got a 43/10 ratio on the diffs.
here is my attempt of making one brushless. I would do it different now.
With a lay-down motor-mount. (so the motor sits next to the diff, instead of above.