Hey buddy... Welcome to Flyme forum...
1) Yes this issue about phone number needs to be resolved. I had given this as a suggestion to the developers and hope they remove that option soon. Meanwhile, it isn't required that you enter your phone number. You can just input some other random characters like "00" or "--" etc. to avoid sharing your phone number with strangers and for your bettery privacy and security.
2) We do not have the option of thread notifications through email currently in our forum. But this can be a very valuable suggestion. Please drop this suggestion under the "Suggestions" section of our forum so that our developers may take a look at it and hopefully implement it in future to provide better services to our users...