I don't need to open ports - but set a higher QoS priority so my ping doesn't go up if other processes or machines do network stuff. Thanks for the 8300-8302 part, didn't have that in my rule yet, must have overlooked those somehow!
Yes, the default port is pretty common. Most hosts that run multiple servers are nice too and use a narrow port range closely around that. But still often enough I end up on a server that uses a different port - no idea why people do play around with that, maybe they read a ssh tutorial for beginners some years ago and the idea of "custom ports making everything more secure" got stuck in the wrong place of their heads somehow.
Or maybe there's some reason for it I just don't know - seemingly unrelated servers seem to prefer the same custom ports after all. Maybe I lack some knowledge or some sever_cfg tutorial is the "culprit" here? The ones I encountered most frequently so far are:
5233,5649,6073,8303-8310,11999,47624
... but that list definitely still needs some refining.
edit: oh, now I see! Quite a number of servers seem to be using ports that other popular game servers use as default - maybe because they already have those firewall ports open and don't want to open another one! I'm gonna see if I can find a general "most common games ports" list somewhere and add the ports for those to the rule even if I don't play them - maybe after that I've got almost everything.