Hi Selling for a cause, and welcome to the site.
Well, Don looks like he has covered your initial questions pretty well, so I'll just that it will all come down to research, research and then more research.
I think Planes would be a good place to start, I'm sure you'll find him quite helpful. Stay well away from any drop shipper charging you a membership in my opinion, most are making their money from the memberships, not on the products you are trying to sell for them.
What that of course means is that they don't care if you sell or not because they are already getting your cash, and being that there is no real incentive to help you sell their products, you will usually just end up with over priced garbage that you have no chance of competing with.
Just yell out anytime you're in doubt, plenty here will be happy to help.