Starting your business on ebay is easy - just follow their instructions. Regarding what is the most popular - that all depends. But, if you want to make a mark - don't compete with popular products. Find an underutilized product and bring it to the main stream - thus being the market leader.

There is a person on this forum Doug (goes by thesologuide) who could really help and guide you to get you started. He is very smart and has great business savvy. Plus, this is what he does - helps people like you get started in the right direction.

Business Money Today
http://www.businessmoneytoday.com/