Love the concept and your other competitions listed on the site.
What I would like: More advanced notice!!!! But I see you already have many people signed up.
I also think your safety approach is excellent.
This is the kind of thing that will make freediving last and grow... good work.
Personally, I would vote for:
Water temp: 5-8 C or 16-20 C
No other gear: sorry William!
Funnily enough, the restrictions that you've put in the rules I think will make certain people have better dives that they might realize!
Pete