You are in for such a treat when they get there. Be sure to spend as much time with them as you can without stressing them too much so that they will bond with you as much as they want. Make sure to have their food and water and shelter all in place so that they can just go in their pen and "unwind" for a while. If you use any treats when they are young use only something like Romaine Lettuce or a leafy green veggie (not spinach) and then only in small amounts at first.
Looking at your pen I would suggest making certain that nothing can dig under and get into them. Once they are grown they will be more able to fend for themselves but as goslings they are as vulnerable as newborn chicks or ducklings. Even when grown they will need a safe and secure shelter for overnight.
Oh, and don't forget pictures when they arrive. We are all suckers for pictures.