yes, you an edit the CSS files for your theme within dreamweaver.
they are located in webassist/themes/your_theme
1) when adding a product, only one image can be used as the product image, but in the description, the last toolbar button allows you to add a gallery.
if you create a gallery, you can add it to the product long description.
2-3) the gallery does not support croped images or using a zoom tool.