how do you get player farther away than 100 studs?

Magnitude

Using magnitude can allow you to get the distance from any two parts in studs. You can use magnitude in your case like this: Loop through all valid players like so:

For indexPlayer, Player in pairs (game.Players:GetPlayers()) do
       --do stuff
end

Then within the loop you can use magnitude like so:

if (Character.HumanoidRootPart.Position - Player.Character:WaitForChild( "HumanoidRootPart").Position).Magnitude >100 then
   --do stuff
end

Sorry about indenting, I did this directly on scripting helpers.