Problems with fostering?

Sounds like a difficult situation. Although I don't have firsthand experience fostering, I know several people who do. From a dog care provider perspective, the best way to have dogs get along is to walk them together. However, all dogs will not necessarily get along with all dogs (just like humans). I'd suggest maybe another resource might be reaching out to a foster organization outside of the area where you live, maybe that specializes in that breed, and ask them for additional tips... besides what others may contribute here.

When I introduce two dogs I try to do it in a neutral environment on the leash. And just give it some time. As far as advertising your foster I would go to the dog park and let owners know that this dog is available for adoption or you can use social media like Facebook and advertise that way. I have fostered some puppies and kittens before. How long you foster them depends on what their needs are. Sometimes they just need to be socialized which may take a good amount of time. For puppies and kittens that usually just need fostering up until their spayed and ready for adoption.