Yes MoCA sounds like a good solution for you. It’s really simple. You do need two MoCA devices (think of one as a place for the Internet to get in and one for the Internet to get out to your computer). You can check online and see if your Modem has MoCA otherwise you need to buy two adapters.

If you find that your modem is MoCA, buy one adapter, connect it with coax to the coax near your computer, with Ethernet to your computer, and to power. The instructions will tell you how to pair it with your modem. It’s usually press a button on both sides or go into the UI and type a password.

If your modem is not MoCA, you need two MoCA adapters and it sounds like a coax splitter. Connect the wall coax to the splitter then connect your modem and the MoCA adapter with coax to the splitter. Connect the MoCA ethernet to the modem/router and connect power. Then follow the steps above for connecting the other side and pairing.

I’m not aware of an enclosure that has a problem running with open slots. I have a Synology unit that’s running with 3/8 empty bays.

I can speak to the Synology RS1221+ as I own two. They are great NASs but they are terrible at compute/transcode.

You missed an important detail which is how much data do you need to store?

Those big servers are nice and powerful if you can stomach the power bill.

My current setup is the two Synology’s in an HA pair for storage with a pair of similar spec Hyve servers for compute. If you’re looking for an all in one unit, the big server is the way to go.