"When both suggestions will be implemented, teams can't vote on players who became first in the previous mentioned rankings. Otherwise players can also get rewarded twice."

Have not seen this problem... The voting should start in the last 2-3 days of the season.. The first places aren't decided yet in that period.. That's why I came up with this:

The player who ends up first in one of the rankings can't win the golden boot, so all his votes won't count when gathering all points for the winner of the golden boot.