1) Cost to install Pentaho 9.4 Community Edition - no cost, though for commercial implementations is highly recommended obtaining the Pentaho Enterprise Edition, which has continuous Service Pack updates with security vulnerability fixes and improvements.
Please note Pentaho 9.5 Enterprise was released in May 2023, and this December is expected to be released Pentaho 10.0 Enterprise release. Therefore relying on Pentaho 9.4 CE for commercial use is not best choice as newer components and libs are available in the more recent versions.
You can experiment the Pentaho Enterprise version via 30 day trial from HV website, or Amazon Market Place or Azure Market Place original Hitachi images with in cloud deployments.
2) There are several types of repository, one of the most popular is Postgres. The installer can do that for you or you can configure and existing one. There is documentation on Hitachi Vantara website about Pentaho installation and configuration.
Hope this helps you start on the best path for you. Contact our Hitachi Vantara experts for a quote by explaining your use case and need. They will help you address your need.