Before you get carried away with how to build the site, I think you need to think a bit about the economics of this business.

1. What would you charge someone for postage? It would have to be less than UPS etc., otherwise there's no point not using them.

2. What would a driver earn for carrying a package? Some amount of money not greater than the postage charge (otherwise you'll go broke).

3. For what amount of money would a driver think it is worthwhile to pick up this package, or several packages, and deliver them to where they need to go? Surely more than just a few dollars.

4. What are the extra costs of your business, such as insurance?

I don't know the answer to any of these questions, particularly postage (I don't live in the US, so I don't know what the cost of sending a parcel is there). But you might want to think about it.