Hi. You need to ensure that your contact page uses a html (or php) form rather than a direct email link, or you'll be innundated with junk mail for years to come.
Depending on your locality and what you intend to sell, I'd also be inclined to include a 'terms of trading' page, where you outline policy on sales, refunds, shipping and privacy.
Whether you have separate category pages will depend purely on how many products you are offering for sale. Unless you have more than about twenty designs, it may not be worth having separate categories.
You need to keep your site focussed on its intended purpose.
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