My first advice about trying to plan a trip involving far-flung people with different ideas, different schedules, different budgets, etc. within the next 6 months is "Don't". There's too much risk right now to make it worth the effort planning.

Beyond that....

1) If you're going to do some of the organizing work, let it be your choice where & when to go. Consider input from others, of course; you want people to join you! But understand that you're never going to satisfy everybody.

2) I recommend against booking people's travel to/from the destination for them. Too much financial risk. But at the same time, be clear about how firm the dates are and be ready to help people select appropriate itineraries. For example, if you're going on a cruise that departs Sunday morning everybody should plan to arrive at the port city Saturday evening (or earlier). It's no good if someone flies in Sunday morning, arriving an hour before the ship departs, because the flights are $200 cheaper!

3) Consider what the plan for lodging is. Are you all sharing a big rental? Booking rooms at the same hotel? Booking rooms "wherever" in the same city? Each approach has pluses and minuses.

4) Once you're all there, what are the activities? Does everyone have similar interests and energy levels? Frequently in such groups people do not, so I prefer an approach of planning certain activities for everyone combined with free time for people to head off in smaller groups.