Making a custom Receipt Printer

Hey, I want to make a custom receipt printer for my mates company, it needs to be as small as possible! I have found a company which will 3D print my housing, but for now I want to see how the electronics would work.

I have found this Thermal Mini Printer which I can use for the printer itself: https://www.adafruit.com/product/2752

However they also sell the guts of the printer separately if that would be easier: https://www.adafruit.com/products/2753

Now what is...

Making a custom Receipt Printer