Some video players can open .mpls files (usually found under PLAYLIST folder), if your video player supports that you probably can see chapters.

Mkvtoolnix for converting bdmv folder to mkvtoolnix without re-encoding.

Deep packet inspection is a thing, AFAIK people in China uses a software called v2ray to counter that.

I currently have Pulsed Media seedbox, which has SSH access (no root) and docker, haven’t tried something like plex/jelyfin so I can’t tell how well it works.

• You should google the name if you want to try them, negative things pops up.

• Password authentication can’t be turned off for SSH.

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.

Stats from my seedbox (all public torrents)

Uploaded: 638.311 TiB

Downloaded: 29.120 TiB

Ratio: 21.91

Which announced removal of port forwarding.

https://www.ivpn.net/knowledgebase/general/do-you-support-port-forwarding/

I setup syncthing from seedbox to my NAS.

https://netboot.xyz/

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

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.