I haven't sold clothes personally, but I would suggest offering the biggest range of sizes possibly would increase your chances of sales.
One of the biggest difficulties I see with a product of this type is that the customer isn't able to try the clothes on, so you have to make the buyer feel as comfortable as possible in making the purchase. Think of yourself as the customer, what sort of information would you be looking for in a listing.
A full size chart perhaps, not just a size, but also measurements as well to assist the buyer. Great pics would be beneficial for sure, they want to see what it looks like being worn, front, back and sides and so on. Put yourself in the customer's position when designing the listing to give yourself the best possible chance of encouraging a sale.