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I have to agree with Heather SEO begins waaaay before the SEO phase.  Here's a link to a post that we wrote on our blog, that might help you out. http://www.theedesign.com/blog/2012/web-design-for-seo. Basically like Heather said, you need to be thinking about SEO every step of the way.  I have no problem building a a blog before hand to help build your audience, but make sure that they are aware that you have a website and you are building towards it.  It sounds like that you're going to be using the blog of "Blog.com" as a blog until it turns into the ecommerce site you want it too, if so make sure you let your audience know what's going on.  Maybe create an email newsletter, so they can get updates every step of the way. Remember if you get links to your website, to pages and articles that arn't going to be there in the final design you can 301 them to keep the link juice, BUT YOU WILL NEED TO 301 THEM. Maybe for the time being also consider directing your fans to a Facebook page or a Twitter account to help build your community. Hope these thoughts help.