As far as the Z97 chipset which is 3rd/4th Gen, i7-4770K or the i7 - 4790K are the best CPU's for that Generation if you're talking gaming.
The 4790K is still a great chip for gaming and gets the job done in 1080 or 1440 depending on the title of course and supporting hardware.
this is the fanYou can reuse your fan that you're using now with your 4590. Are you using the stock intel cooler?
Yes you will need new thermal paste. Any brand is good, personally i use Grizzly Kryonaut.