Maybe the biggest challenge in business is to know your future customer. It's one of the few things you do not have much control over, although it's a basic need of a business.
The challenge you face here is to describe the customer segment you are going to target as detailed as you can.
First you will need to do research on who are likely to buy your product and service. you can check out the competition (always a good idea), collect relevant statistics (demographics, psychographics and topographics) and define potential segments based on the data.
After having an idea of the segment, it's good getting an image of future customer. From the data you have gathered now, it should be possible to create various personas that are most likely to become your client. It's quite fun to do, and will help yo set a right tone in the website content.
With all this information you should be able to get to a good definition of what kind of website and products your customer will want.