I read about the tournament and felt sad. It's a shame that it was mentioned so delicately after it ended and didn't actually take place! I feel sorry for the respected Alan, who organized it but didn't get any results.
For example, I didn't know about the tournament because I rarely visit the section for game 3; I find the section for game 5 more interesting.
I think 1) it would be good to inform the tournament organizer that a tournament will start in, say, 10 days. Users don't visit the forum every day, so they'll have time to gather people.
2) It's still a good idea to create a list. The organizer indicates the list in the first post and adds to it. Those who want to participate can write to the organizer in a private message so as not to clutter the topic. The point of the list is that if a person has signed up, they will feel awkward letting others down and making excuses. People will simply remember them as an unreliable person; of course, emergencies are possible, but I agree that this is rare.
3) The most important rule is to have one General save file to start from. In my opinion, there is no other option.

Regarding save files... This is probably the most difficult part. It's unlikely that you can avoid putting pressure on people. Send the final save file, and in case of controversial issues, ask the participant to send the save file from any day...

Good luck with your new endeavors! Sincerely, Gmir.