The server uses very few resources, except when processing videos (it uses ffmpeg). In general with 2-4 GB of ram and 50GB of space should be enough for a long time (3-4 years of data). Nostrcheck.me now hosts 40.000 pictures and videos and the data usage is about 9GB.

You can stop the server, but your multimedia files will not be available to others, your notes with images or videos will not be seen (unless you use something like cloudflare, in its free version).