Power BI Desktop is a perfect first choice for this scenario.
Certainly for the first phase, to figuire out what data to use and how to transform and display it.
In a later stage you can move the data model to an (on prem) tabular model on the sql server. You can keep the reports in a Power BI desktop file.
It will soon be possible to publish Power BI reports to an on-prem sql server. (this feature is currently in preview (requires sql 2016)). Then sharing with other (internal) colleagues is also possible.
Then you have a great on-prem Power BI solution.
Cheers, Edgar Walther
ITsmart BI and Analytics consultant
Power BI User Group Netherlands