I'd keep them seperated at first when you are not home to supervise no matter how well they seem to get along.

You seem to be going about this the right way, Kudos to you!

I'd say to go ahead & give it a try. If you are really worried about your dog & are not prepared or can not handle a dog if they do not get along I would make sure you make that clear to whomever you get the dog from. Make sure that the shelter/rescue organization will allow you a trial period or allow you to return the dog.

The only other thing you may want to consider, if you do get another dog that is very close in age & breed, to be prepared to loose 2 dogs at about the same time. That may too much for some to handle.