please meet this little guy and be SURE. As you've said, he's already lost two families, his next one needs to be a FOREVER home. Now I'm sure that's what you are planning on, but I would feel irresponsible if I didn't mention that. (forgive my rescue mommy blabbering)
Also, if you decide to have the two meet before you make your decision, please don't put too much stock in that encounter. When we decided to adopt Bernie he'd lost his original family and was living with a very loving foster family (so to him he'd be losing two family's in the short year he'd been alive). Hubby and I judged him on his own merits and kept Ginger (and Kirby and Fun Kitty) out of the equation. If we were committed to this dog, then we were committed to making it work at home.
Dogs don't always take to each other immediately. Or they can have a blast together until the "home-dog" realizes the other one is here to stay. I've had multiple furkids in my home for 25 years...it's not always love at first sight between fursiblings.
Buy some good books on introducing a new pet to an established one, and allow time for them to be best buds...it may not happen immediately. (Ginger loved Bernie immediately, until the first night...about two weeks in we decided it was time to let him sleep in our bed...ack! She didn't like that one bit).
We've worked it out.
Good luck. I wouldn't be too concerned about the seperation anxiety. It sounds like you are good with working with these little ones and he seems to not have too many other issues. Of course, meeting him will be your best indicator.
P.S. Another cool thing about adopting a dog (instead of a young puppy) is that there personality is more "concrete" and you can get a better idea of who your dealing with.
Bless you and I hope this works out.