Mapping modules
Ok, I have the beginning of an answer to my question 2 (the only one that’s technically hard). It would be tempting to just add a text field asking people where they come from, but it turns out the clean way to do this is to run mapping modules that geocode correctly that information. I found a recent comparison of mapping modules on the Drupal website. Earlier this year I did a seminar on geodata. The teacher advocated Leaflet (visualizes against OpenStreetMap instead of Google Maps, which is probably better for Edgeryders commitment to openness); apparently, installing the Leaflet module you get an option in Views to output the view as a map. Sweet!
I am asking around for a recommendation as to which modules to use.