You bought a great buggy, don't go too cheap out on electronics.

You can use your TQI transmitter if you really want to, but I highly suggest looking into a different radio system . Something like the spektrum DX3c would be a huge upgrade and it is not very expensive.

Savox servo's are the best bang for the buck out there. A 1256tg or 1258tg would be a good compromise of performance and price.

For ESC's, I would use a XERUN 80a or 120a depending on motor. These are under a hundred bucks and are some of the best 1/8 esc's out there.

http://www.hobbypartz.com/07e-c-xeru...FUjZQgodV0sALQ

Motor wise, I do suggest running Tekin if you are going to be doing any racing. Very smooth and powerful. Th3 1900kv or 2050kv buggy cans will work perfect with 4s batts.