1. On the product details page, is it possible to open the image up larger in a new window also?

We use the jquery image slider from http://www.jssor.com/.  In order to find out if they support a popup to a larger window you would need to contact there tech support.  Or if you are a programmer you can change the image gallery to anything you want by modifying the viewset http://helpdesk.smith-consulting.com/kb/a1453/managing-viewsets.aspx

2. On the product listing module, can we modify how many items display i.e defaults to 3 across so that the photos are larger. We are happy that it can either be in a grid or list format.

Yes, in order to modify the product list you can modify the viewset and change the bootstrap css to 3 across or whatever you desire.  Here is an article on how to modify RazorCart viewsets http://helpdesk.smith-consulting.com/kb/a1453/managing-viewsets.aspx

3. We would like an image / banner slider on the home page in addition to the featured products slider. Can you please advise if this is possible. Also to have the image full width of screen.

RazorCart has a built in product slider you can use (http://helpdesk.smith-consulting.com/kb/a1541/product-slider-for-razorcart.aspx) or you can use any image/banner slider from the DNN store.  If you use the razorcart product slider all the products will be dynamic (read from the DB).  If you use an image/banner slider from the dnn store you will have to enter your products manually and then link to the razorcart product details page or cart using a querystring variable (http://helpdesk.smith-consulting.com/kb/a1543/querystring-variables.aspx)