Always build in a social element: lunches clubs, beers, dinners, stammtisch, etc.
Once you have a core set of contributors
one face-to-face meeting a year will help solidify relationships
Meeting face to face makes it easier to build a community It builds trust and mutual respect And helps build a community hat can withstand conflict (which will happen) IF you can make your community a friendly place , where people's opinions are taken seriously and are acted upon, THEN individuals will work harder to convince their management to stay engaged with your package and make more contributions. IF it is NOT a friendly place , with no trust and respect built, they may contribute something and then move on.