The most important thing to consider is your competitive advantage over others that may compete for the same type of eCommerce store. Low barriers to entry is both a pro and con to eCommerce.It can be incredibly competitive, and the competition makes it harder and more expensive to acquire customers. This level of competition also drives down prices.
The first step to starting any business is research and planning -- in this case figuring out who is already selling the goods you plan to sell. Look at what they are doing well and where there might be opportunity, and then figure out what your niche will be. Determine how you will build this niche into a big enough segment of the market where you can meet your business goals.
This preliminary research will ensure that your investment in eCommerce is well spent and you have the best opportunity to be successful online. If this sounds intimidating, consultants like Atlantic BT can help you analyze the market and plan strategies to win online.