Hi, I have 2 3D Printers which I consider myself to be more knowledgeable with them than my CNC Mill.
3D Printers, although following the same motion principles as a CNC Mill is a different beasties altogether.
I stand to be corrected but although both 3D Printing and CNC Milling uses the same code family (Gerber G-Code) they are two completely different flavours.
You will need to control both Hotbed and Extruder temperatures infinitely. Temperature control is a critical element to the printing process.
For my money I would purchase a Controller Board from Fleabay (circa 40 quid) a heated Bed plate and a half decent Extruder. And using a GNU public licenced software package like ReplicatorG (Free !!) you should be on your way. Good Luck!
as an additional thought, there are plans and drawings dotting about on the web which will give you some insights into building a DIY Printer, some are a bit Heath-Robinson but one or two are quite well designed.
Keith