If you need more ram but not a lot of CPU a used thin client can work, i use a HP t630 since 6 months now with only nextcloud and storage, has 2 ddr4 slots and 2sata m.2(not Nvme) for Expansion. Again its a 4core Pre Ryzen AMD chip so don’t expect any Wonders. https://www.parkytowers.me.uk/thin/hp/t630/ this is a good side for this and other thin Clients.

Edit: according to HP the idle Power consumption is ~12w

I had them once named after things ( mostly Ships) from Jules Verne Books: Nautilus, Albatross, Formentera, Duncan, Dobryna, Hansa.

I had this exact idea but for old Consoles: every PS4 could be a perfectly capable x86 Computer, 8GB of Ram and a AMD CPU, enough Power for Office and Web for a long Time. Only Problem the Software.

Can you reach the dockercontainer? i have used docker only once (without any Proxy settings )but i had to specify which ports from inside go to which on the outside, something like: “docker run --name docker-nginx -p 80:80 nginx” https://www.digitalocean.com/community/tutorials/how-to-run-nginx-in-a-docker-container-on-ubuntu-22-04

You don’t need a Own Domain, you can use a dynamic-dns-service to reach your server from everywhere, even if your ISP changes your ip. I use dedyn.io. (its free) here is a turtorial: https://desec.readthedocs.io/en/latest/dyndns/configure.html