OK, a couple of responses....first, on your questions....

On your question of whether the data changes, there are 2 general physical modes for data in PBI....they go by slightly different names, but they are basically "direct query" and "in-memory compressed"

With direct query, every time your user interacts with PBI, it's going to do a query against the source.
With in-memory compressed, you retrieve data based on a snapshot schedule (could be every hour, twice a day, once a week, etc.)

While the direct query might seem great (real time access), PBI visuals won't be nearly as responsive.
When you use in-memory compressed, and set a refresh schedule on the server where PBI is deployed, the PBI visuals and overall user experience are better.

Bottom line, trying to use PBI with real-time access is very tricky and potentially very problematic.

On your question of deploying, you have 2 options:
- If you have SQL Enterprise AND you participate in Microsoft Software Assurance, and your users will all be internal users, you can get Power BI Report Server for free. It's basically like deploying SSRS reports to an internal report server. PBI report server itself is free....but you have to have sql enterprise AND Software Assurance. The biggest thing I don't like about this.....while PBI Cloud gets enhancements every month, they only release the report server 3-4 times a year, and even then, there have been features in the the cloud version for a long time that still haven't quite made it into the Report Server. I got fed up

- If you don't have enterprise / SA......or you have users outside your domain, there are different pricing models for deploying PBI to the cloud. There's a learning curve, depending on how tightly/loosely you want to tie your PBI reports to any applications. At first PBI to the Cloud drove me nuts (and still does), but it really is the way to go.