Adopt 2nd Child? Age & Finances vs Single child

I personally don't have experience with this, but one of my very good friends and her DH decided that, after one adoption ,they were finished building their family for many of the reasons you listed in your post. Their dd is 6 now, and they are all very happy. They are able to go on vacations, they are living comfortably, and their dd is not wishing for a sibling, although she does occasionally ask for another dog ;)