well to start with read this website: https://chocol3d.com/
It'll add on to most i3 printers.

Multi material/colour - two main options.
The prusa mmu and the mosaic.

Personally I reckon the mosaic is a better option. But the mmu is easier to fix/modify tourself as well as being cheaper.

You'll want a DECENT i3 - so up your budget.

I really want a car that changes into a boat for £50 - but alas they actually cost about £150,000 ;-)