I currently use immich with 40k+ files.
I think what OP meant by ‘early development’ is the updates with break Changes.
Ive been using immich in docker self hosted for 1.5 years.
I use authentik for user management and single sign on.
The breaking changes have only ever been minor changes I’ve had to make to my docker compose file, its always come back with no issues after the well described changes in the release notes and several of the changes I didn’t even have to do because it did not apply to me.
This is petty standard stuff for anyone used to self hosting but if that sounds like its not for you then check out the roadmap. The stable version is expected next year sometime. Wait for that before giving it a try.
Personally I like the fast development, I find myself likely and using at least 1 new feature ever major update. I think this will easily become the best photo manager in 1 to 2 years and it will not longer be much of a competition
I’ve recently started using a kanban board which has been working well for me.
There are several options, I use obsidian for this because I can easily make a task into a note for further details.
Not FOSS of course but the .md file are easy to access and backup and i use the self hosted live-sync plugin to sync between 3 devices