Best practice to implement stores
We used OG extensively in many sites with stores that are auto-created when a user registers.  You can check out one of them here - www.craftsaid.com - each "store" is an OG.  We also did the same thing on Bandromeda.com.

Install Organic Groups Module - http://drupal.org/project/og
Install Rules Module - http://drupal.org/project/rules

After you have created a content type for your Group type (this can be anything you want it to be - if you're not familiar with OG it is an incredibly powerful platform that allows users to create groups to which other members may subscribe - essentially you create one content type as the "group" type itself and then any other content type can be set as "group content" that may be added to a given group) go to /admin/workflow/rules and add a rule for Event = After saving a new user account with an Action = Create a new entity with parameters of Entity type: Node, Content type: Your Group Content Type, Title: [use tokens to create your title configuration] 

This will auto-create a Group upon registration.  Otherwise you could simply create a link to node/add/store (or whatever your group content type is) from wherever makes the most sense in your site.

That is a very basic explanation - there are probably 50 ways you could implement this to accommodate your general description of your need.  Hope that helps!