Have a separate database for data warehousing?

I have built a typical web application using PHP and MySQL for enterprise usage.

The MySQL database is 3NF as much as possible.

However, as time goes by, the requests for the data appear to be more for a data warehouse so that they can slice and dice the data in whatever way they want.

Hence I picked up a book the 3rd Edition Data Warehouse Toolkit of the Kimball Group.

Inside the authors described a Kimball DW/BI Architecture and using star schema for dimensional and fact tables for DW/BI purposes. See below.

My question is, since I am most familiar with PHP and MySQL, should I have the data warehouse star schema in a separate database from the original 3NF database?

No commercial BI tool will be used. Anything that looks like an OLAP or BI would likely be an open source software that I may augment myself.

Please advise.

EDIT

My entire 3NF MySQL database is currently about 20mb so far growing about 1 mb every month or so.