This is such a fun, engaging take with a familiar structure. JUST my cup of tea. You've done such exciting world building, too. I would love to see this develop. Count me in!

As for including multiple kinds of characters, potentially consider building in teams of workers who cover various responsibilities. Exploration, communication, engineering, community planning, and so on. Perhaps some pop through these little pockets, these gates, and explore while others work to maintain contact and keep reports up to date regarding what the exploration teams uncover. Maybe some teams deal more heavily in the politics of planning how to introduce others to the concept and reality of the transition, all while tackling, "who can go in/how can we settle/who has priority?" etc. You can expand the "cast" by giving some vague [i]group titles[/i] or teams for character creation purposes. In using some loose restraints, you can make sure people create characters that will serve the plot, while also not keeping the play limited to very few people doing a handful of things.                 

Sorry to blither on, but I hope this little chunk of thought has a thing or two you can steal and build upon. Love this idea!