FCM API Limits (40M web push/day)?

[Travis M]

Hey, I need to send 30-40 million web push notifications per day.

All the tokens are stored on my own server (not in realtime database or anything)

A send delay of ~1-2 hours is OK

I need the messages to be individualized/personalized, so I CANT use broadcast.

Question 1: Does FCM have API rate limits? What if I just spin up an Elixer/Erlang node with 500,000 workers and I just concurrently hit this endpoint with async HTTP requests? https://firebase.google.com/docs/cloud-messaging/http-server-ref

Question 2: If I'm storing all the data, what will my pricing be to use FCM?

Question 3: If the above WONT work, what are my options? I saw something about "FCM Server" but I'm not sure how that works or if that solves my issue.

Thanks