question

The meters are discussed in more depth in the documentation (https://docs.microsoft.com/en-us/gaming/playfab/features/pricing/meters/meters), and in particular in the best practices guide (https://docs.microsoft.com/en-us/gaming/playfab/features/pricing/consumption-best-practices).

As to where to write your data, it depends upon how much data you have and how often you need to read and update it. The best practices guide talks about this a lot more, but in general, if it's large data that's rarely updated, Entity File would be your best bet.

As to "users per title", that only applies to the free tier, which is limited to 100K total user accounts. To have more than 100K users in a title, you would need to push that title to the Live state in one of the paid tiers of service.