I am still very much a novice in the self-hosting space, Linux etc. having fairly recently switched from using macOS as my daily driver and not tinkering much at all.
One of the things that often confuses me is networking and making sure my setup is secure. This is currently holding me back from hosting more stuff locally that I would require access to from outside my home, as I am afraid I am doing something that could severely compromise my data. It can sometimes be difficult to follow explanations from more advanced users due to the many different components of networking and security, and different layers of abstraction, which prevents me from following completely. I might understand one particular case, but then be unable to make connections to another one. So I would want to research this more intensively, and ideally I would end up being able to easily understand the data flows - the paths the data takes (e.g. I make a HTTPS request to some server from my laptop, how is that traffic routed correctly through my local area network and later the wide area network), in what forms (i.e. different protocols, encryption layers etc.).
In communities like this, I see there are a lot of very knowledgeable people who maybe could recommended any resources that cover this from the basics and onto more advanced stuff? Maybe a textbook from a university course on ICT that is considered particularly good? A YouTube channel with great explanations and visualizations? I am looking both at home LAN and internet in general. Enterprise level networks are not very interesting to me (at the moment).
Thinking about the torrent thing, there's no better way to do it. I'd personally open a static port IE 12345 and point that at the torrent client on the PC. I would not randomize it and open a massive range on your firewall just in case. Then just close the client when you're done and know that packets for 12345 will still reach your PC, they're just dropped there.
Not that I support it, but if you're downloading more then just Linux ISOs and you're in a country with pretty strict laws around this sort of thing, you should be using a VPN that supports opening ports. then you do not need anything open on your firewall, just to connect to the VPN when you're ready to sail the high seas.
UPNP should be disabled on your firewall (unless you play xbox or whatever). This allows a device, like an xbox or PC, to request your firewall open a port. This is needed for some online games to work properly but is not very good for security.