It's here ヽ(´▽｀)ノ

Emma, one of the top players in any% uses this 'https://github.com/MCMrARM/mc-w10-version-launcher/releases/tag/0.1.0'. Haven't personally used it, but others did and it worked

Hi, happy to see someone interested in this category. Hope I can help with answers.

1. Yes, you can play with more than 2 players as no other runs have been submitted yet. When someone else will submit we'll probably have to split the boards because we don't want to make it 'most popular wins' type.
2. Preferably one player should get all achievements, as it's easiest to verify and not make it a puzzle where I need to put all pieces together. The person who gets all achievements should also be the host and record, which leads us into
3. No, only the host needs to. They will need to host the world to prove no cheats have been used. Also they should get all achievements on video. But if more players will record in one video I would be ok with it (and as a watcher I would love it). I think as long as all achievements are on video, the host is recording at least and you don't cheat you should be fine. Looking forward your run :)