Ryzenhasrisen :
Eximo :
From everything I can tell they are basically standard MicroATX boards with SFF power supplies. All looks to be standard ATX stuff.
Front panel connectors are sometime slightly custom in OEM computers, usually just a matter of re-wiring. Though if you are building a case, then you could just use the case's front panel headers as is.
For such a system, I would say a GTX1050. But really anything you want to spend is pretty well supported. Maybe not something like a 1080Ti, but a 1060 wouldn't be a bad match for 1080p gaming.
I'm not very familiar with them because i just recently got into building pcs. but are refurb kepler cards worth a look?
Well that includes a lot of cards. Some are still pretty decent. 780Ti and down to the GTX650. All depends on the cost/performance. I've seen a few people picking up GTX770 for quite reasonable sums, those are a little faster than a GTX1050Ti. GTX750 and GTX750ti are actually 1st gen Maxwell cards, so there is a significant technology gain there.
Just keep in mind when buying older cards, there might come a time when you want to run something new and won't be able to. You can always upgrade.