You need to do some planning first. You need to come up with 1-3 sizes that you guarantee all the images will obey to in the product section as I wrote before. Or 1 size, but since some of the images are portraits other landscapes and some near squares, i suppose 3 would make the most sense. I am not gonna bore you with mathematical equations for setting up proportions.
You can chose one size for all the thumbnails or you can chose 3 sizes it is up to you. Since you are not selling plastic baubles you will need to prep your images prior to uploading, unless you want to gamble on wordpress.
What I mean by that is that wordpress has no concept of cropping and will ruin every single image if you let it , so unless your collection is as numerous as the Hermitage archives, you will need to resize the images yourself *prior to uploading* them to ensure no heads are cut off. I resized the image below myself first so I made sure it fit the way I wanted to.
Here , I tested one of your statues Thanksgiving, it is normally 300dps (which is meaningless online) and 5000or so pixels width and length. I set the program for 330x330 without crop http://i.imgur.com/ffEllEC.png
and this is what came out:
shop -> http://www.clipular.com/c?2249657=5lk3qS2XfqgjLOugSace5TgFqlw
product page -> http://www.clipular.com/c?2247734=27ZeixszuukQraAoRH7RhYqntjg
On your page http://www.sanzencollection.com/shop/mother-baby/ I think you are overloading the images and instead , each of your product pages should have attached pages with a full length slider that profiles each piece and has content , or poetry or something else along those lines.
Also dont forget to use the portfolio, since you can create a sortable portfolio of thumbnails sorted by categories and then instead of being taken to the portfolio item page , the visitor can be taken directly to the store item page.