"Market place type thing" and charities that won't reply to your emails do not a plan make. You have great intentions but I think you need partners in this, and you should delay launch until you can formulate a real plan for what you're going to do with this, your website is complete, you have partners, a 501(c)3 setup, all the things that make a charity "real".
It's admirable to see an 18 year old take initiative to support a cause that's obviously close to his heart, and well done with progress so far, but you need to work a lot more on this before launch in my opinion.
can you contact me on skype: mtwiscool