ClassiPress already has the Ads and Blog section included, so that part at least is fine. In terms of forum functionality though, this as you know, not built into the theme, but you have options. You could go the route of trying to integrate the forums via SimplePress or a phpbb bridge as others have done, or you could install a
WP forum such as bbPress in a different directory to ClassiPress, and link the databases in order to allow customers to register/login once (instructions for this are on the bbPress website). So yes, you could technically implement everything into one ClassiPress installation if you had some coding knowledge to take care of those unsupported issues such as the forum plugin and any other tweaks.
You could technically do the same thing with the "News" section of your site, if you wanted a different news based theme to ClassiPress for your main homepage. If you were using a WordPress theme for all 3 sections (Homepage, Classifieds, and Forum), then you could look at a WordPress multisite setup.
e.g.
yoursite.com <== Whatever theme you like
yoursite.com/classifieds <== ClassiPress
yoursite.com/forums <== BBPress
This would be a setup that would involve the least customization anyway, if that is your biggest concern. We have many customers who actually do have existing websites and do not wish to lose their homepage, so this is exactly how they too could use ClassiPress in conjunction with an existing site.
