Just another loop to find the users with 4+ tokens, then grab a random token from the result...
Code:
  var %i = 1, %a
  while ($hget(TwitchChannelUsers,%i).data) {
    if ($v1 >= 4) { %a = %a $hget(TwitchChannelUsers,%i).item }
    inc %i
  }
  if ($numtok(%a,32)) { did -ra GiveawayTokenController 33 $gettok(%a,$rand(1,$v1),32) }

You shouldn't need to set %currentgiveawaywinneris as that info will be in $did(GiveawayTokenController,33)