You can find information on how to install and set up ClassiPress including video tutorials
here in the ClassiPress documentation.. As a paying customer you will also have full access to these forums where you can find support for any installation and setup questions you may have, including a specific thread for community support of customizations.
Which licence you buy depends on what your intention is for installing ClassiPress in terms of number of installations, whether you want the footer credir etc..
The buy page here will give you more information about what each licence covers, and the price.