Obviously! If you intend to sell to the traffic you worked hard to get, write proper descriptions. It's digital merchandising, no different than real life. If you're out of ideas, create a list of questions for the copywriter to answer for each product. Think of things people would be most likely to ask a sales clerk if it were a real store. If your products are all related, recycle some FAQ's and have the writer answer them, then spin the content to vary the keywords. Presta has some SEO plugins which are highly recomended. If its not too late however, I would suggest you look into opencart. It is superior to Presta in many ways, cheaper to develop using oDesk people and has amaaaaaaaaaazing seo tools that dont cost too too much. There are wonderful templates that are easy to write copy for - Shoppica is one, others are on Themeforest.
