The SD card write protection is only intended for very special use cases. Functionality errors could occur in combination with, for example, the Squeezebox Server or Kodi. This is because these services may need to be able to temporarily write to the SD card in order to run correctly. Therefore, we recommend using the SD card write protection only in special cases.
In principle, the Zero W should work with Bluetooth. However, the Wifi and Bluetooth modules get in each other’s way. Even with a Pi 3, we found that either WiFi or Bluetooth did not work optimally when both were used at the same time. Therefore, I would not rule out the possibility of such connection errors occurring with a Zero W.
Adding repositories via the web interface should have the same effect as adding them directly in Kodi. However, we haven’t touched this feature for a long time, so it may be that there are problems with the new versions of Kodi by now. Adding the repos within Kodi should work in any case.