Wordpress is good for creating websites as it offers a stable framework.
SEO considerations are the same as those with a blog. So long as your content is unique, of high quality, navigation is simple, then you'll be fine.
One benefit of using Wordpress as the basis of a website is that you can add supporting content easily in the form of posts which link to your main pages, thus increasing the chance people will find you through long tail keywords.
Handling members of a site is easy using plugins like Wishlist Member or
Magic Members. You can also run your own affiliate program using
Affiliat Royale or
Magic Affiliate.