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 Bus Matrix where I keep my 3NF database and I have a separate database which is meant for data warehouse which of course is designed in a star schema.

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.