As someone who has a server rack with multiple servers, I would not recommend them to start with as they use up a ton of electricity. I'd recommend a small form factor computer (or a mid sized tower) to start with, it'll be marginally less powerful but for what you need it'll get the job done perfectly fine.

If you have an old desktop laying around, that's the perfect way to get started. Even if you only have some old parts, that'll cut down on your initial costs. For anything new I generally recommend looking around at places like https://logicalincrements.com to see what they recommend for CPUs and motherboards at different price points. For hard drives I use https://diskprices.com and also eBay. You generally want motherboards that support 4+ SATA connections or have PCIe slots for an expander in the future.

A lot of people start on used small form factor desktops like the ASUS PS52. Other common ones are the Lenovo M series tiny desktops, Dell Optiplex micro desktops or Intel NUCs. These can sometimes be found used for sub $100 a piece from businesses updating their fleets. They can struggle a bit doing stuff that needs some CPU grunt, like live plex transcoding, but are decent otherwise, especially considering the low power draw. You might want to consider spreading that software demand over two or three of them.

Just an idea. You could try hosting and using these apps on a VPS from a cloud provider to find out what your needs are.

I personally just use an old desktop (4th gen i7, yeah that old) and a NAS (mostly for bulk storage seperated from the server). The device you listed is probably more than enough to handle everything, unless you're sharing Nextcloud and/or Plex with a bunch of people.

Have you looked into an actual NAS rather than a mini-pc though? It'll give you more storage upgradeability over a mini-pc, and a quality NAS could probably host everything.

I would also consider buying used, especially first starting out. You can save some money buying a model year or two older hardware for decent savings.

Pn52 is not a bad choice. Very upgradeable. Gigabit networking is probably all you’d need.

The heat may become a problem. But I dont run one so wouldn’t know.

Run proxmox on it. Your sweet 👍

What size drives are you thinking if you plan to host a plex server? Whatever you think, I’d recommend doubling it.

I upgraded my gaming machine and used my old motherboard and cpu and loaded unraid on there, the i7 was great for plex transcoding and eventually i ran out of sata ports on my machine so I stuck a sata expander card in my one pcie slot, luckily the motherboard had two m.2 slots so I used that for cache. the case I used was a node304 and over time I added drives as I was running out of space. eventually I build a separate JBOD chassis to hold more drives

HP EliteDesk 805 G8 💪

Not too shabby TBH. Still have a concern about the storage thought. Since PN52 can only have 2 SSDs and 1 HDD, RAID is out of questions.