Got a few thoughts on this. Stood my S1 Kermit next to my S5 Gonzo next to my S4 Rizzo, and here's what I think.
Gobo and Red about the same height of Kermit, especially since that's what Ken said of the Gobo prototype painted sculpt he has in the office.
Mokey, slightly higher/taller than Kermit.
Wembley and Boober: Boober with magnetic lucky hat slightly taller than Rizzo, and Wembley slightly taller so as to reach the same height as the arc of Gonzo's nose. Or Boober would be just as high as the tip of Gonzo's arching nose, and Wembley would be just as high as the point where Gonzo's nose is placed or where it starts coming out of his face.
Cantus could be as high as Piggy, and the Doozers could be articulated PVC figurines.
The Gorgs could all be cheated to be either the same height as Sweetums or slightly taller or shorter depending on the character.
Sprocket would have to be as tall as Swedish Chef with his hat on and laterally wide, probably placed with his feet up or down in the plastic bubble.
Philo and Gunge could be the length of the Lobster Bandidos, and then the Trash Heap could be fully-formed or emerged from the ground base she'd come with. The Trash Heap would probably end up one of the bigger figures, on a par with Dr. Phil van Neuter from S8 and/or Bobo the Bear Guard when/if he gets made.
Hope this helps and have a good day.