Questions about a mining rig

I want to start small and then expand. Is it possible to use a regular PC case with two cards and then when I want to expand to extra cards I can build a second case/riser rack outside and run the power/pci connections through my regular PC case to the mainboard?

Also....do I need to use all of the same type of card or can I use different cards? Say one 1080, two 1070s, and add vega cards when they come out?