You may wish to consider the following: unless the subdomain is a standalone site, having your SS store as a subdomain will not give it any Search Engine Optimization (SEO) benefits that your main domain currently enjoys, such as Page rank, ranking in the Search Engine Results Pages (SERPs), etc.
This means you will have to build up the SS subdomain as a brand new site as far as SEO goes.
This is not much of an issue if, like me, you have a generic domain name and each subdomain is intended as a brand new standalone site. However, if you have a well-established site with good organic traffic, you may wish to consider setting up your SS store in a subdirectory instead, as in
www.yourdomain.com/store, as opposed to store.yourdomain.com
Similarly with any blog you wish to set up.
HTH...