Hello Sha,
Instead of admin demo we have a
user manual at this forum, which may help you build your store.
1. I believe if you are familiar with html and css it will be quite easy to customize the layout, colours etc.
2. Yes, the JV stands for Joomla Virtumart as you might read it at the Boss Cart website. We used these open source cms in order to provide an effective shopping software. We worked a lot to transform Joomla much user friendly, and grabbed the Virtuemart among the components an upgraded to a fundamental part of the script.
Thanks