That could easily be changed to any other port, most home firewalls are capable of port forwarding.
I haven’t seen a single router that is unable to accomplish this in many years.
It will point inbound connections to the Pi, but unless you’re running a web server, that’s completely meaningless. No internal to external internet traffic would be impacted
Setting up a server to reverse proxy the connections is above most peoples capabilities, port forwarding is not that much work (though I don’t advise putting your Pi directly accessible from the internet.
Way more complicated than the above, but still the most secure way to achieve remote connectivity.