Sourcing the parts

First thing you want to do when you order your printer kit is order 2 of these 3D Printer heat bed Mosfets. Just google it, you can find them for less than 5 bucks.

You need 2 of these, so you can use one for the heating bed and one for the hot end. They are usually only meant for the heating bed, but work great for the hot end as well.

Speaking of hot end, get one of these nice E3D V6 Bowden extruders ($20):

Make sure it comes with the wires and the white Bowden pipe, i.e. as a kit.

I upgraded the power supply as well to one of these (12v 30a DC Universal Regulated Switching Power Supply 360w, $20):

LJ12A3-4-Z/BX 4MM NPN DC6-36V proximity sensor:

That's about it to get you nicely set up in the beginning. You can get all the parts from Gearbest, Banggood, eBay, or Amazon.