Firstly;
CPU was between the 3570 or the 4670, I went for the 4670 as it was only $20 more. Good choice?
Yes. Go with newer tech.
Motherboard - no idea here, read some reviews, this seems OK. Thoughts?
Seems OK.
RAM - Open to pretty much anything, but this seemed OK.
Also seems fine.
Next;
Where do I head next?
CPU Cooler: Never had to consider this before, usually bought a bundle. Help please.
You could just stick with included cooler. If it's too loud, you could go with CoolerMaster 212 Evo.
Cooling in general: Some general cooling suggestions would be very much appreciated! Not interested in liquid
Front and side fans are intake, Rear and top fans are exhaust. You don't need to fill every fan mount.
Storage: I have an old WD5000AAKS 500GB SATAII I can recycle, but may consider an SSD for the OS. This is low priority for me.
Try SSD, you won't go back. Don't need to go bananas. I used a 64GB Agility 3 for a long time before moving up to a 256GB Vertex 4. Use the 500GB for media storage or any other overflow.
Video card: Not a clue here. Help? I currently have a XFX HD 5850 1GB Black Edition which I bought for a very good price, but no idea what to get now!
Don't know what to suggest- I still use a HD6950 and it works perfectly fine for me and the games I play. GTX760? HD7950?
Case: I've never been into flashy cases, I can probably recycle my *really cheap* current case - is there any advantage to paying more money for a case?
Technically a good case would provide better airflow as well as run more quietly. And also, it would probably have USB3.0 headers.
PSU: I have a Coolermaster Silent Pro Gold 600W currently, I can upgrade if MOAR POWER is needed, though.
Nope, no more power is needed. I run a core i7-4770K, 3 drives, wireless, etc on a 550W Seasonic.
Optical drive: Have a DVD drive, never use it, will recycle current or buy a cheap alternative if needed.
Just recycle it so long as it's SATA.
OS: Windows 8.1 64bit Pro, already have it.
Cool.
Displays: Recently bought a new monitor, don't need a third/to upgrade.
Peripherals: Have a Logitech G510 keyboard, Logitech G400 mouse, Razer Kraken headset - more than happy with these, no need to change.
Wireless: I have a wireless NIC I can use, but I use powerplugs and I'm in love with them, so absolutely no need.