[Si Coe]

Your batteries will be fine for now, I'd use them till they start to puff up (you'll see) and then replace.

There are plenty of decent esc's out there at not too silly prices. You want a 120A esc ideally - which can be had for around £70 if you get a Hobbywing Xerun V2.1. Its an older model but has an excellent reputation. The Sky Toro TS120 is a few quid more, and more modern.

If that sounds a little steep Speed Passion do a combo of the Reventon R esc (70A) and their 7.5t motor for £75. Its a cheap way to get all the stuff needed, but that motor is right at the limit of what the esc can manage. OK to start with, but you'll want to upgrade further down the line. But then you'll probably want to do that anyway!