Anything with a clearance of 12" 30Cm is fine for that gfx card
check out lian li's stuff, fractal do some understated cases too,
plus you can always mod an alarm to the system to help prevent theft
Yup, Hdd cages are removable if the Gfx cards too big, which it shouldn't be
Psu is fine,
and are you overclocking that 2500k?
you will want an aftermarket cooler like the H212 if you are, unless of course you fancy watercooling?
With a *good* watercooling setup you can achieve lower temps than with air and thus higher OC's. I will say that it has been through much research that I have come to find that *most* of the self contained watercooling setups such as Corsairs H-XX series do not offer much if any lower temps than comparably priced air cooling solutions, but when you start getting into the double 120 radiator setups and custom jobs then you start seeing the performance.
Yes, real watercooling, although the costliest option, and often a hobby all by itself is the best cooling generally, the allinone units like H100's are comparable to highend aircoolers, and can often be outperformed by them, price vs performance there would tell you to buy the good aircooler
I run custom water and love it, not because I need it, because I love the engineering processes in designing and building a loop, the actual benefit is a nice bonus ofc,
but decent water kits start at around £130, and I usually suggest higher end kits or bespoke loops so its not the cheap option here,
I would look at a good aircooler for now, and maybe save £300 for a decently performing loop later
more money is always better in W/c
as long as its spent cleverly ofc