The real raised question is IMHO "is C3 usable without Rex (and R0J0 etc.)plugins" ?
No it's not. Unless you keep your games fairly simple. Anything more complex and you're gonna need those plugins or code your own.
danlei looks like you only have half of what you need. there's still hope he comes around and decides to support his plugins. Or someone else ports them. Which raises the question, if he has abandoned them, is it ok for someone else to port his plugins to C3?
Yeah I'm out of luck for now. Though I can work without firebase in the beginning. Just need to do a lot more manual work and make some very bad workarounds.