I would recommend making a separate bank account for group buy money. Next I would research the rates your bank charges for USD to EUR conversion. Most banks don't give you the most favorable rate. Also look into the procedure for starting an international wire transfer.
Also, make sure you're very specific on how people fill out the order form. This will save you lots of time when you get to shipping.
Charge a little extra on everything. There are going to be costs that are not apparent at first (customs charge, USPS price increase, etc.)
You can order flat rate boxes on the USPS website. They will be delivered to your door for free. For international, you can order bubble mailers on Amazon Prime.
I would be happy to help you out in any way I could, just let me know