Just my 2bits regarding 3 day rides in which I've participated.

Organization should include a planned breakfast every day at a specified time.

Plan and organize a lunch one day (usually the first or second day) and a dinner for one evening. Even if everyone pays for their own meal this lets everyone know when they will get together. Also, this still leaves time for impromptu groupings to try that diner they saw down the road.

Have rides of different lengths laid out and mapped for folks so they can decide how long they want to ride.

Plan the ride for no earlier than mid-June nor later than the first week in August. Otherwise it starts bumping up against school dates for teachers or parents with kids in school/college. Also that time period only bumps against one holiday so that no one has to choose between sacrificing a Labor Day or Memorial Day weekend versus a ride.

Its liable to be hot no matter where you ride in the summer. The Hotter-N Hell was 65 degrees at start time this year.