some sort of dashboard with monitoring and statuses of all my services

See if Uptime Kuma suits your needs.

Are there any major no-no things a newbie might do with Docker/selfhosting that I should avoid?

Allow password based SSH authentication, you should look into key based authentication

I wanted to have it behind a domain, how would I achieve it?

Use a reverse proxy (like caddy) which serves different content based on domain name.

https://netboot.xyz/

You might not need it but it’s a very small image (3.5MB for multi-arch iso) so why not?

Official wiki page that lists AP with Wifi AX support

(Some devices that lists “Snapshot” might be supported by 23.05 currently in release candidate phase)

If I remember correctly you can plug in phone line to RJ45, this stackovwerflow question lists some caveats.

I setup Swapspace in case I ever need to compile something very big, but usually my system doesn’t use swap.

Serverhunter is a search engine for cloud servers and has easy to use filter functions.

I am surprised that I didn’t see anyone link to https://lowendtalk.com/ and https://lowendspirit.com/, OP can ask in both places and see what people have for offer.

Gigabyte GB-BNIP-N200

MSI Cubi N ADL

Beelink EQ12

I’ve saw some good news about Intel’s N95/100/200/305 CPUs, N200 is said to have similar performance as I5-7400 at 6W TDP.

If you mean automatically update IP part, duckdns website has a very comprehensive guide.

If you mean getting a free SSL certificate, you can use acme.sh (this is what I used) which has integrated support for duckddns (To use let’s encrypt you need to use --server letsencrypt in your command)