Suitability really depends on what kind of functionality you want from your site. ClassiPress does not have a built in feedback system, so if you're posting ads for products, then the only option for people to give feedback would be to comment on the ad itself. Outside of this, it would require some customization on your part if you were looking to do something more comprehensive like a rating system. Yes, registering users can register with their own username. No, there are no character limits.
If you do not have any coding knowledge, then you would be limited by the functionality of the theme, and therefore may find it frustrating if you cannot find a non-coded workaround for the features you want.
I would think that possibly the
Vantage theme could be better suited to what you describe, however this theme has not yet been completed, and at this stage there is no confirmed
release date available.
