Hi Will,
#1
You can return items by going to the orders menu and refunding the order. You can select specifically the items that you want to refund. (does not have to be the entire order) http://docs.shopify.com/pos/operating-pos/orders/complete-refund-orders#refund-order
#2
The dymo barcode scanner you have lined will allow you to import products via csv from Shopify and print barcodes for all your products. We will likely be adding tighter integration down that road, but this should be able to get you up and running.
#3
What did you want to report on specifically on Register Shifts? You should be able to generate reports on your payment types. When closing a register shift, all your payment methods will be totalled for verification. Is this the case?
