you do not need to set up subsites for this functionality. You can do this simply by implementing simple personalization system. You can do so by taking advantage of the ASP.NET membership, role and profile providers which are used in Sitefinity. You can find more about these topics from here:
Basically, you would have to create a few controls which would be aware of the currently logged in user and depending on its user name controls would display appropriate data.
The personalization is too big of a topic and beyond the scope of our support, but we'll be more than willing to help you with any specific problems in which you may run into. Feel free to contact us again.
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