Depends where and how you want to run it.

For general bashing around in the dirt and occasional rock use, any waterproof BL system will drop right in. Most I've seen use 3000-4000kv range. Low gear helps with the cogging of a sensorless system and it's not as noticeable.

If looking for more trail and rock use, go sensored, though waterproof sensored is a bit harder to find - you can do it yourself if you're so inclined. Brushed might be better in this scenario.

There is no receiver box stock. You're on your own with that one. Traxxas box or the tried and true balloon would be the way to go.

Any "shorty" battery can fit, and 1/16 packs work great. I use Traxxas 1/16 packs and they work fine. I like the smaller packs as it's less weight out back.

Be aware it does not handle high speed high grip situations at all, even with the swaybars. COG is just too high...any kind of pavement running is sketchy. It's a total blast in the dirt though.

That all I have, I tried the high speed thing and didn't care for it. Mine is set up for rock/trail duty only. 35t brushed, single speed converted and locked diff up front.