[is it legal to kickoff with [EDIT:]MORE THAN two players in the centre-circle?
They had 3 players in the circle - which is unusual, but probably not illegal. (stupid typo, sorry!)
]
I think so
"Kick-off
• after a team scores a goal, the kick-off is taken by the other team.
• all players must be in their own half of the field of play
• the opponents of the team taking the kick-off are at least 9.15 m (10 yds)
from the ball until it is in play
• the ball must be stationary on the centre mark
• the referee gives a signal
• the ball is in play when it is kicked and moves forward
• the kicker must not touch the ball again until it has touched another player"
From the Fifa website. Other websites mention the attacking team not having more than 2 players in the centre circle but from my interpretation of the above they are incorrect.