On large outdoor tracks a 6.5T is usually a good idea - if you decide to race modified. Any halfway current model from any reputable brand should do in modified. Stock classes are more choosy.

For an ESC, i'd go Hobbywing myself - I've been using them for years and like them a lot. XR10 Pro G3 is the current one, I believe (for Mod). BTW if you run mod, use timing or turbo options thoroughly.