I must admit that I had similar thoughts as Hyacinth about whether adopting a dog that may just be a bad match to yours is the best thing to do. I would find it absolutely heartbreaking to send a rescue dog back, but it is a trial for a reason. Maybe there's a place for lovely Rusty with a dog he gets on with straight away. And maybe there's another rescue out there that would make a better companion for Reef? Maybe he would be more accepting of a female?
But whatever you decide, I'm sure with your experience and dedication you will make the most of it