unfortunately bbshowcase was for the standalone version 1 of bbpress and doesn’t work with the wordpress plugin version.
As suggested, I copied all the template files inside bbPress plugin directory to my active theme
Not sure where you got that from. Only if you want to alter templates do you need to copy templates to a bbpress directory, and then only those you wish to change.
Also, how do I remove Topic: and Forum: slug at the title of the page?
Can you specify exactly what you want to remove – a screenshot would be good