An open port is not something that you find, like a buried treasure. It’s something that you set, like a thermostat, to whatever you’re comfortable with.
You pick the port that you want. Look, just pick 65432. Why? Why not? Because I said so. Because it’s hard to forget, you start at 6 and count backwards. You already spend more time fussing over it than it’s worth.
If you’re using the Windows built-in firewall, then turn on “ICF” in your BitComet preferences/options/whatever. If you’re using a third-party firewall, uninstall it, use the Windows built-in firewall, enable ICF in the P/O/W. Having done this, BitComet will automatically open and close the port in the Windows firewall, for you, and you can forget about it.
This isn’t nearly as hard as you are making it. The words may be unfamiliar but the concepts are simple.
You say you don’t need a router. Ok, good. You don’t have a router, then you don’t have an EXTERNAL firewall in that router. So you don’t have anything to forward a port through. If you don’t have a router, don’t have an external firewall, then you don’t need to set up a static IP – port-forwarding, static IP, all of that applies only to people using routers. None of it applies to you at all.
You MIGHT have a software firewall running on your computer, that you don’t know about, but that’s a separate issue. Your ISP might have your connection behind a firewall, and if it does there’s nothing you can do about it, but that’s a separate issue.
The one thing you absolutely do not want to ever do, is to connect to the Internet without a firewall. Do you get unwanted spam in your email? Most of it comes from people just like you, who connected without a firewall, got their machines compromised, and are unaware that they’ve been zombied, serving out spam and DDOS attacks at someone else’s command. These guys don’t want to wreck your machine. They want to keep you fat, dumb and happily ignorant while they make money off your computer and your network connection. It only takes a few minutes to be infected and zombied. Don’t connect to the internet without a working firewall.