Your eCommerce website design is particularly important and has much more to it than just producing a great looking website. You should take care that the platform of your choice is SEO friendly and that whenever possible the company designing your site is responsible for the SEO, they are hardly likely to make things harder for themselves. A responsible SEO company will start with a mixture of the long tail and short tail keywords, the long tail keywords will get your organic traffic moving more quickly and the short tail will get you the volume later on.