I think definitely PowerStore is an excellent starting point to for your cart and check out pages. As far as image uploading I think PowerCMS is what you will need to use to upload images and other things. As far as Galleries i think you should look at the PowerGallery Solution pack (powergallery-demo.com/) which should help you in creating different galleries.
With a little bit of work you should be able to integrate these solutions to work together by using the same database.
Although PowerStore might not have all the features that you need, but it could jump start you on Users registrations and log in, products and check out, order managements, users managements and much more. (powerstore-demo.com/)