I have 4x 4TB HDDs and I want to build a DIY NAS. I was curious if the H370M from ASRock, i5-8400 and 16GB of DDR4 would be a good start?
I just want this for streaming my media and basic backup storage.
A couple things here.
What OS are you planning on using for this system? Windows, FreeNAS, or XPEnology? Take a look at what NAS vendors are using for hardware and that will give you an idea of what to go by, but base your decisions on what platform you intend to run. FreeNAS and XPEnology will run on much lesser hardware than what you are spec'd for, while Windows will need more.
I would recommend you research XPEnology since you are wanting a NAS build for media and basic storage. If you decide you want more enterprise features, then you can move into FreeNAS.
If these parts are something you already have, all you need to figure out is how you want to interface your storage. Onboard RST or is their a RAID card in your future?