I am very interested in building a new PC with a mini-itx case for portability reasons. Specifically, with the cooler master elite 120 advanced case. Within this case I intend to have an i5-2500k as well as a gtx 670 (or 470 depending on whether I upgrade or not from old systems). I probably will aim for 8gb of ram.
Here are my questions:
What kind/size of power supply can fit in a small case like this? I don't suppose I can fit my corsair hx 850 psu in there?
Also, what kind of HDD can I fit in a case like this? Do I need an ssd or will a standard hdd fit just fine?
I'd scrap your plans - that kind of hardware will not fit in an mITX system and still be able to have adequate cooling. A full size ATX PSU - modular or not - will not be able to fit in that small of a form factor. You won't be able to use a plastic water block either, you might be able to use a top-down fan but that would be cutting it close.
If you want that kind of a system you might want to check out the Falcon Northwest Tiki or Fragbox.