My process has been:

1. Be annoyed at ads/payment structure/whatever in some app or service
2. Search https://alternativeto.net/ for alternatives to the thing I’m annoyed with (filtering by Open Source and my devices)
3. Try out 1-2 of the top alternatives
4. Settle on what service I want to run
5. Install, route the subdomain, etc. if necessary (otherwise just access via my tailnet)

Hope this helps!