That is not correct. A VPN would be one method but you can also just expose the service to the internet in a number of ways and accomplish the same thing Plex provides.

No. You have to expose your server to the internet in some way bit you don’t have to set up some sort of VPN. There are plenty of people who will tell you how awful of an idea it is but if you make smart choices it’s not a big deal.

You should build the hardware around what your compute requirements dictate. A NAS needs little in the area if compute power but Minecraft could be a little demanding. Review the Minecraft server requirements and build based on that. Or build to Max out your budget and get the best you can up to that point.

The -R is the recursive switch

I just expose it to the internet.

OnlyOffice has been working fine for me though I’ve not used it in serious capacity.

I initially started with Collabora but for some reason I couldn’t get it working. This is surely not an issue with the product though and entirely my fault.

Just use the wifi then

Set up what you want on what you already have and if your workload is more than your hardware can handle then upgrade.

Overall most of what you rattled off isn’t too resource heavy but 12gb of memory isnt exactly a lot and i dont know what your minecraft server will eat up.

Alternatively look up the recommended minimum specs for each of your desired applications and add up the needs.

Additionally if this isnt going to be a headless system and you want a desktop gui that consumes resources as well.