Long time reader. First time builder (N00B)

I’ve been a long time lurker of JDMs builds and am finally ready to take a leap. I was eyeing up Synology equipment and quickly realized I’d rather build my own for various reasons. I would like to keep the same form factor that Synology uses because I like the small compact frame and the easy access to the drives. I’ve seen a lot of info on the HP290s and have a couple questions about it. So basically I would like to build a mini atx box that has access to the hard drives using the Intel G4900 from the HP290 since it can handle the transcoding so well. Is something like this possible or am I in fairy tale land?

I mostly play locally at home currently using my laptop running 24/7 which I want to get away from. Plus I would like to share with my family in other states (3 other streams). Would need the ability to transcode (which is why I was thinking of using the G4900…powerful and cheap). I am aware that Mini ITX makes this more expensive but I have ~$500USD (without storage) I’m willing to spend. Can any of you nice people help me out?