You will need to buy neu motors directly from castle creations, and medusa's from their own website (
www.medusaproducts.com)
For the Neu... go with the 1105/2Y or 2.5Y. the 2Y is 5200kv, and the 2.5Y is 4000kv. I own both and run them in my detta buggy and ST respectively. And you don't really need to get rid of your sidewinder micro esc. It can handle both motors (that's what I use), but most go for the 1/10th sidewinder since it can handle more amps and is nearly the same price.