I think introducing them on neutral territory, such as your suggestion of walking them together, is a good idea. Does Ollie ever show signs of jealousy? That's the problem I have with Louis, not so much with me or my OH, but with my best friend, whom Louis adores. When we walk our dogs together Louis becomes nastily jealous of any dogs that approach my friend and guards her unless she's quick enough to realise what he's going to do and walks away to stop the situation escalating.
Hopefully Ollie will be more interested in meeting a new dog and making friends with it than being jealous, but please watch out for signs of it.