1) On the cart page, you need to delete the "EditRegion3" string at the end of the editable region.
2) to show the thumbnail, you need to create a thumbnail column in your cart object. Since your cart is static, you need to edit the add to cart button server behavior. On the bindings panel, enter the image name in the thumbnail column.
Then in the cart page, change the image source to use the thumbnail column in the cart, and prepend the image path in front of it.
3) Use the shipped weight. If the packaging will add a significant amount to the weight, it should be included. If it will only add a minimal amount, then it can be left off.
4) To show the selected size in the cart, you need to create a new cart column in the eCart object to hold the size. Then in the add to cart button, on the bindings panel, select the size column and set it to be updatable from a select list.
This will add the size select list to the page for you, you can populate it with the sizes you wish to offer.
When you create the cart page, make sure to include the size in the list of columns to display in the cart display manager.
