If this is your first hackintosh attempt and there is no specific guide to follow for an HP 600, it's normal to face problems like this. I've written many guides for HP and Dell pre-builts that are complete step by step guides. I've never owned an HP 600 or 800 G1 to test on. I'm not exactly sure why you have these problems.
If you want to try a Dell 7020 or 9020 SFF there's a Golden Build guide you can follow that is guaranteed to work. It uses the same Haswell i5 CPUs and same DDR3 ram you're using now. You could even buy a low cost barebones with no CPU or ram and install your CPU/ram into one then use it.
You could even use a lower cost 3020 SFF and follow the guide for that.