I think that Stefan and Proxi would definitely at the very least be friends. They seem to have a good bit in common as far as work habits, intellectual pursuits, and being left alone. Plus Proxi would probably love to observe his carbuncle, Esper. ๐
Stefan is a kid (well heโs 25 so not really a kid) that hasnโt given much thought into relationships. So friends at the very least. He could always use someone he could speak on the same intellectual level with. He doesnโt have very many friends.