1| Finding a board for your Haswell refresh processor would be hard but you can
look through this shortlist. I'd side with the Gaming 5 matx board by Gigabyte and
a case to go with it. Less than 200USD.
2| What sort of a form factor are you looking for? If you're going for the single most powerful GPU load out then you should look for an mATX or mitx setup.
3| The memory controller, although initially stated by Intel to be backwards compatible with DDR3 rams, was revealed to be glitchy and damaging to the system when paired with said DDR3 DIMMS thus the way to go with Skylake is DDR4 kits. Haswell processor's memory controller will only work in tandem with DDR3 kits.
If you're yet willing to go with mATX then
this board alongside the aforelinked N200 chassis will be a solid performer albeit the need to shell out for an i5-6600K and a DDR4 kit.