Power BI Embedded for ISVs questions

We are evaluating Power BI as a visualization layer for our application. 

Our primary data source is elastic search, and our front-end is in angular 4.

Costs:

I've reviewed the Capacity information, and don't really understand the meaning of "Usage"? 

Does it mean that if a customer user accesses our application, and the application serves up a dashboard, report, or tile and the user spends 30 mins on the page - we, ISV, pay for 30 mins? If they then open another application without closing the power bi embedded application for the next 30 days - are we still paying for usage when the page is idle?

What is the role of the "capacity sku"? Is it basically compute, storage, RAM ...?

Does it store the pbix files and the data?

What refresh cycles are available for the data?

Can refresh be triggered by events?

Thanks in advance for any answers folks might have!