Thanks for trying reef-pi. I'm glad to hear that it's useful for saltwater and freshwater tanks! I'm sure Ranjib will jump in, but here's my take on it.
1. You can control multiple heaters with a single temperature probe by adding multiple probes in the UI, but choosing the same sensor. You may need to stagger the check frequency when doing this. reef-pi v2 doesn't have hysteresis, so if you set the heater threshold to 25, the heater will turn on whenever the temperature is less than 25 and turn off as soon as it exceeds 25. reef-pi 3 is adding hysteresis, which will allow you to do as described.
2. We're still working through some significant changes in lighting (and anything PWM related). The API supports saving multiple profiles and switching between them, but it is not implemented in the UI yet. We're working to get as much of this in and tested before the final release.
I've really enjoyed helping with reef-pi, and it's been a pleasure working with the other devs. We have a set up guide at
https://reef-pi.github.io/additional-documentation/development/. We also have a slack channel for dev conversation. I'd love to see more hands on the project if you would be interested.
The error you are seeing is probably a side effect of upgrading to 3.0. It introduces some significant changes and is not backward compatible with 2.0. Ranjib introduced some db commands, so you may be able to fix it, but it's probably easier to
delete reef-pi.db and reconfigure.