Is there a reason I shouldn't use gitea locally?

550 stretches. Use amsteel.

As others have suggested I would stick to internal only until you're comfortable. Dealing with automated port scanning from all over the globe is a nightmare if you aren't running a tight ship, and a collasal headache to deal with if they get in. I started with pihole, jellyfin, and some other simple docker services. Check out linuxserver.io if you go the docker route, they have good prebuilt compose files for you to use and the community has good info on their forums. You don't need a domain but it's preferred if you want to host something public-facing. Make sure you have fail2ban configured if you open stuff up to the web, it makes dealing with the automated attacks easier.

Tree style tabs. Leaving 100 tabs open is a sign you don't know how to use a computer.