Communication is via discord. The WTRL TTT is a bit of a hack workaround so there's a real process to getting the start right - half the fun.
Teams can be mixed ability and graded accordingly. The main thing is working together well. If there's an A rider then probably put them on the front for long turns but not pushing threshold for drafting B/C/D riders in the team.
It's fun but so popular now that sometimes the wait in the start pen can be very long, over 10 minutes.
If team was new and couldn't check their Zwiftpower results, I'd say a reccy ride as a group would be almost essential.
Four. Only three need to finish. But the more the better up to 8.
I've raced with three before and it's fine but hard to get a solid time.