Gday Mick,
After your experience last year, I know where you're coming from.
I've almost never been a solo traveller. Trips are very social for me - great way to make friends and get to know people.
I have my own rules according to how long the trip is:
Weekend trips: doesn't matter who comes - nice to mix it up and make new friends, and throw in a few beginners. Up to 20 vehicles in the right location is fine.
1 week trips: Most people get on
well and don't get touchy. Limit 10 vehicles. Mixing some experienced travellers with beginners is good.
2 week trips: ideal length for a desert trip in my experience. People get to know one another pretty
well in that time. If they get touchy, they may find a reason to do the bolt for home a little early, but no big deal. Limit 7 vehicles.
Longer than 2 weeks: need to pick the people very
well or break the trip up. Limit 4 vehicles. For these trips, I only go away with people I know from personal experience are good, relaxed capable travellers and
well prepared with a good vehicle.
"Respect" is most important in my opinion. If respect for the leader is lost, or the leader lacks respect for the participants it will be a fizzer.
Cheers
Phil G