Nope, I pay 1.99€ / month for 100 GB. No more, no less.

Nope, I have free 15GB, 2GB x 2 times Security Checkup Bonus from 2017 & some; & pay $20/year; and have total 100 GB (so paying for 100-15-2-2= 81GB)

I only have/pay for 100 GB. It's also possible to share the storage with other users.