Firebase maximum projects and apps
As of now (8 Dec 2017) I got a maximum of 5 projects
I got this message when I was creating new project and only had my 2 existing projects.
You're 3 projects away from the project limit.
I occasionally create a new Firebase project to test and learn its new features such as Firestore and Cloud Functions and then delete the project. Last month I tried creating a new project to learn Firestore and only had 2 existing projects, I've never got any project-limit message like this before. I think Firebase team just changed the project limit to 5 recently
Update 8 March 2018
My account reached the limit. I tried request another 10 projects to Firebase team and it took 1 business day to approve (sometimes it might take longer). I have to say that Firebase team is not mean. They are willing to help if they can.
I request a project limit increase and say I want another 10 projects because I'm starting my new startup(MVP) and want to keep the cost low at first. After the business generate money I will pay for Paid Services. Besides I told them how easy I can reach the limit as I have to create new projects to test Firebase features, like Firestore and Cloud Messaging before using the features in production. And finally they gave me another 10 projects :)
If you want to start a business with Firebase and have already reached the limit then Firebase team is going to help and give you project limit increase as long as you're not a spammer.
I just searched this because I was watching a video which hinted that you can only have 6 free projects:
https://youtu.be/VUNkjQ_k2Uc?t=1m21s
It has three created and says you can create 3 more. The video was recorded/uploaded 13 Jul 2017.
I guess it wouldn't take much to confirm this if you just created six test accounts.
Update from here:
There is indeed a quota on how many apps can be created in a project. The exact number depends on multiple factors, but it typically is in the lower 30s.
The quota cannot be changed, nor is it increased for paid projects.
How many applications can I create in one project from a single account?
I don't think there isn't any limit on how many apps you can link to a single project. AFAIK, I think it is actually encouraged for apps that are related when it comes to the Firebase services to be linked to a single project.
How many projects I can create in Firebase for Cloud Messaging?
I'm not sure what you mean for the for Cloud Messaging part, but I'm pretty sure that every project you create can be used for FCM. Anyways, I think it'd be safe to refer to the comment by @FrankvanPuffelen on this post:
There's no limit on the number of projects in general, but there is a limit on the number of projects on an unpaid plan. The exact limit for that varies, from what I understand.
PS: As per looking around the docs, I'm fairly sure that there is nothing explicitly mentioned/stated in the official documentation that can clearly answer your questions.