Depends on the type of track you run at (your profile doesn't have a location) as to whether you'd prefer the balance of the TQ or EC - my first Xray buggy was an EC and as already said, they're pretty much bulletproof! Great 1st buggy to learn with as you can crash them all day and it'll still finish the race.
As to what needs doing, it depends on what the condition of the buggy is overall - all driveshaft pins and diff outdrives that they sit in will wear over time and use. You can replace the pins which cuts down on wear. The rings and pinions on the diffs are very robust so long as they're shimmed right.
I'd download a copy of the manual off the main Xray site, if you don't have one, and spend some time getting to know how the buggy is put together.
Replace the diff and shock oils so you know what's in there, follow one of the setups on here as a starter for 10 based on the track you will be running it at.
That's it really