Happy to answer your questions :)
All CGS limits are free tier limits as we are in the testing phase. Construct plans will get more generous limits, and there will be additional paid tiers with even higher limits. We’re still working out the details of all this so bear with us. We’re introducing a new broadcast service soon, after which we’ll be neatening everything up and releasing the plans before adding more services.
Regarding the message when you login, you can set your own oauth secret keys under auth settings on the left menu in your CGS account. Some are very easy to customise, some are a lot more involved. This allows you to have your game as the sign in message with each oauth provider.