Fun fact for tiny build fans, Ethernet cables have a minimum length to achieve their stated performance.

Yeah. They won’t support it if you have a fault so keep the default in a box somewhere, but it’s officially kosher to provide your own. You’ll get a box on the wall (ONT) that turns PON fibre into gigabit ethernet, and that you have to use. But it’s essentially a media converter. DHCP is all you need, no authentication/login - your ONT authenticates you.

Used to work there. It’s fine, esp on the newer builds which you’ll be in. XGS-PON and usually plenty of backhaul capacity. Router’s crap, chuck it and buy something decent, same as any other ISP.