I can speak in general terms about a nitro -> electric conversion.
1. Yes, the 2 speed will go. Not really needed due to the difference in power delivery between nitro and electric. Generally you run a center diff that is pretty stiff but does have some give to it (7k is a decent starting point but others may chime in with a more chassis specific recommendation.) Do not run it locked up.
2. If there is an electric conversion kit available, go for it. Much easier than trying to cobble something together and then run into parts availability later for something that was custom.
3. Battery. 3S is really the min I would recommend for a power source. You can always run your 2s in series to make a 4s pack as well (I do this for my 1/8 regularly). Higher cell count means more volts means less amps are needed. Less amps means happier electronics.
4. Motor and ESC. Depending where you are running (space, racing, etc) will determine what motor to use. Anything from a 2200-2650 works well imho (preferably sensored) but depending on area/speed/battery might be too much or not enough. The 2200kv is a good middle ground that lets you start with 3s and go to 4s if needed later for more speed. ESC - I do like the RX8 and the Hobbywing (as long as you run an external bec). Might give the nod to the hobbywing as its a bit smoother and cheaper. Both will do fine on 3s and 4s (and beyond if needed).
Hope this helps.