I'm not aware of WFDF rules regarding spirit circles (then again I haven't played at the WFDF-level).
EUF requires (or at least used to require) teams to also do spirit circles before the game to set expectations. Read about it here:
www.ultimatefederation.eu/posts/the-powe...-game-circle-119.php
Regarding your questions:
1. As said before, I don't think there are specific rules. The way I think works best is that teams huddle up for a minute or two among themselves to see if there a any special things (good or bad) that should be highlighted so that the person making the speech can talk for the whole team. Then teams form the spirit circle right after that.
If there are any important issues that weren't adressed in the spirit circle but came up when one of the teams did their spirit scoring, the spirit captain can go to the other teams spirit captains and let them know or discuss the issue with them.
2. That depends whether the tournament is sanctioned by WFDF or any other governing body. If it's not sanctioned by any governing body it can also make up its own rules regarding spirit circles.
3. If I understand the question correctly, see my answer to 1 (although that's just my personal opinion).