Overclocking on that motherboard is really limited and I believe gigabyte limited the voltage to 1.2v. The z series are much better suited to overclocing with full control. I'm kind of confused as to what you're doing, first you're considering a z series board because of overclocking limitations then ask if you need an aftermarket cooler if you don't overclock. Are you planning to oc or not?
Since you mentioned you have a small case, make sure you have adequate airflow and a decent/good aftermarket cooler (that will fit your case) if you plan to overclock. Smaller cases, heat builds faster and usually require smaller coolers depending what case it is. I'd look into a z series motherboard, there are z97 matx motherboards for around $100. No fiddling with bios updates, vrm's capable of additional power used for overclocking, full oc control in the bios etc.
Before diving into a bunch of parts purchases, consider if it's for fun or if you need to overclock (can't imagine it bottlenecking anything). If it's worth the increase to you from your current setup to justify a $30-50 cooler plus a $100 mobo. If you're using an oem version of win, you may or may not have to buy another os license when swapping the motherboard since it requires an os re-install. Search around for some devil's canyon overclocking guides, there are several good ones that help explain various settings. You'll want some monitoring programs like hwinfo64, coretemp etc. If running prime95, make sure to use v26.6 and small fft's for steady workload on the cpu. Newer versions will cause the 4690k to run excessively hot beyond normal stress and I wouldn't personally recommend it on the stock cooler.
http://linustechtips.com/main/topic/41234-intel-haswell-4670k-4770k-overclocking-guide/