Help with a random team selection system

[georgeface]

Hey, I'm trying to make a gamemode where one team, the Hunters, are randomly selected and their team makes up 20% of the players online (e.g 10 players on server, 2 become hunters, 20 players on then 4 are hunters) any help with this would be appreciated, it's the only thing I can;t figure out :'(

Also is this right for getting players to spawn as Kleiner or Breen based on their teams?

[lua]util.PrecacheModel( "models/player/kleiner.mdl" )
function team_1( ply ) --Set Team 1

ply:SetTeam( 1 )
ply:SetModel( "models/player/kleiner.mdl" )
ply:Spawn()
end

util.PrecacheModel( "models/player/breen.mdl" )
function team_2( ply ) --Set Team 2

ply:SetTeam( 2 )
ply:SetModel( "models/player/breen.mdl" )
ply:Spawn()

end[/lua]