Setting up an e-commerce website is very simplified now a days.
With a lots of hosted platforms and cart systems you just have to research and choose from the one that is best for you and will give the best support.
Site uptime and look and feel of the site are also important but having said that you should also consider hosting with enough resources so as to handle expected traffic.
Last but not least, getting into an e-commerce space you need to analyze your sites positioning in the market
for ex. I would like to discuss the case of one of the projects I'm working on <a herf="http://www.dressmyphone.in">dress my Phone </a> offering Fashionable mobile accessories in the Indian gadgets and accessories market.
Your Value offering in term of the products in this case cases and covers should be such that it should be closely related to the search trends so that it isn't that hard to drive traffic.