1. "Unlimited websites" means that if you purchase a theme, you can install it on as many websites as you wish. It does not mean access to all available themes - that is the AppThemes Club Package more information can be found on the
pricing page).
2. The Photoshop .psd files are useful for web designers who wish to redesign the layout of the theme, as they contain all of the layout/color/size information for all of the pages used within the theme. You still need knowledge of .css in order to make use of the files, so if you do not, then you may not find a use for them. You can also always upgrade from standard to developer at a later date if you do need the files. There is no demo for these files. Thanks.