The mail address is not the issue. You can enter any address you want there if you don’t care about Let’s Encrypt being able to reach you in case of problems (they won’t).
Don’t be afraid of the logs. You don’t have to read or understand every line of them. You have an issue with your certificate? Search for certificate and read the lines above and below to get clues what might have gone wrong.
The easiest thing: We use a motion sensor to automatically turn on the light for the stairs. You wouldn’t need Home Assistant for that, but with a little more configuration you can adjust the light levels and colour temperature based on the time of day (not as disturbing at night). We have two rooms which have problems with humidity in one a fan is automatically turned on (basic) in the other a dehumidifier is triggered based on the outside and inside temperature because there are large windows which are producing a lot of condensation otherwise. Now the really specific stuff: My daughter has Diabetes and we need to manage her blood glucose levels. There are alarms but ideally you would act before they are triggered. So we hooked her blood glucose levels to a light in our bedroom which turns on if her levels are getting out of bounds at night. That way she isn’t woken by the alarm, but by one of us and can go back to sleep much quicker.
That’s easily Home Assistant. It got me into the whole home automation stuff and I have gradually included more and more parts into it - including some health related stuff. It really makes my family’s life easier and helps us organizing it.
I just spun an instance up using the docker compose file. I did disable the exposed ports for all the services except reitti itself. Is there a specific reason you keep them exposed?