In addition to advertising, the next two that jump right at me are transactional and subscription-based revenue models.

In terms of your second question, I think it's a very intriguing and out of the box thinking model. Marketplaces in general are very challenging to build traction on. Not only do you have to reach the point of liquidity (not to mention tipping) quickly, you have to do it while juggling other areas of your business. My recommendation is to not spend too much time in engineering your platform, you can simply tests out the concept by building some ad pages and see if there is demand. From there, just keep optimizing your funnel to see what's working and what's not.

In concept, I like your business model, but I do see some inherent challenges. Primarily, how do two people in your platform that are looking to barter, agree on equitable terms? If you're not using money as a common form of currency, what will you use in its place? How do you keep yourself from policing transactions when the value perception is intangible?