Can i create a site using the theme and switch to plugin?

You can absolutely do that - the way our theme and plugin store the data is the same (uses the same database fields) so you can build pages in the LiveEditor of the theme and then transfer over to the plugin version later.  

The only thing to bear in mind is that with the plugin version your "normal' Wordpress pages which are created by going to Pages >> Add New - would adopt your thesis theme styling once you have that installed - but any LiveEditor pages would retain their design