Storage will be my issue I don’t have the funds for much so thinking about getting 3 of the following drives (yes I know they are USB but works fine for my unraid setup) in a RaidZ config which I believe will give me 1 drive redundancy: https://amzn.eu/d/bqb10wZ
Was thinking I could find someone to 3D print me a 4 bay toast rack style holder to rest the drives on top of the ProDesk?
The 2 internal drives (256gb M.2 and SATA SSD) I am planning to use as Boot Drives.
I've the same but one gen newer. i5-8500T with 16GB of RAM. I am not using RAID since I don’t want to run it over USB. I run OMV on Proxmox with two weakly RSYNC jobs for backup. Also run Plex/PiHole/Website via LXC 24/7.
15W idle: ~41€ annually
For a homeserver alone you won’t need more than one system with Proxmox. You would save quite a bit of power consumption.
Personally, I'd go down the route of getting a NAS, either a commercial off-the-shelf unit or build you own with something like an HP MicroServer. The Gen8 Microserver is getting a bit old now, but for NAS duties it would be perfectly fine you should be able to pick it up for a reasonable price secondhand.
The setup is not ideal, I won't lie to you. It could be better. But honestly, if it works for you, do it. There are so many things you can do to improve it and generally it will serve as a stepping stone to the next upgrade you see yourself making.
I will also note, since you have two of them, you could take the proxmox route and make them redundant. I am sure there is a way with Unraid to make them redundant too. I really wish I had the knowledge to run things in RAM.