To build a network game on some new platform, the 1at thing is to make a chatroom and now you've made it. And next you can try to build a 2-player version (one uses wasd, the other uses arrow keys) with several sub systems implemented. Then you'll think about how to organize a room/world, ramp up Max players numbers gradually.
Every network game has different bottlenecks and you'll never know what they are before you implement part of it. Moreover, those problems are usually resource dependent which means money can solve your problems ,usually. For example, Counter Strike has 20 for its max players, while a text turn-based mud allows more than 200. If the designer pays for a better server, those numbers could be change.
No matter you choosed MP or firebase, you'll need a always-on Host/Server build by C2. By far this architecture is in unknown water, I never heard anyone who had run this kind of system for some time. If you have any info or news, we'll certainly be happy to hear that.
I don't have other book or article to recommend currently, I'll be aware of this topic and share some info if I find something.
Start your prototype today!