I'd like to handle the creation of character stats atm just to keep things consistent and further establish a 'standard' for Transformers under Hasbro/WotC's "universal D20" miniatures/RPG system.

How good are your artistic talents? Cos one thing that would be useful is actual miniatures, and I don't necessarily mean 3-dimensional miniatures, but 2-dimensional miniatures would work as well. Hasbro/WotC released 2D cards representing characters that had yet to be released as 3D miniatures such as the Reek, Acklay and Hailfire Droid (etc). All you do is get a piece of cardboard (or even paper), the same area as their miniature base (e.g.: 2D Hailfire Droid is a 3x3 square card) and draw a 2D "bird eye's" view of the character.

I personally haven't decided what the exact 'scale' of these miniatures would be - and it's kinda hard because not even Star Wars Miniatures aren't really to scale to each other. As gargantuan as the AT-AT miniature is, it should actually be even bigger if it were to scale with most 1x1 square sized miniature. I'm glad it's not because that miniature is already too bloody big as it is! So an approximate scale would do. The Transformers are pretty tall but their base doesn't necessarily take up that much space. Rumble and Frenzy could happily be just 1x1 whereas Optimus Prime, despite his height, could probably just occupy 2x2 or 3x3 squares. Even Ravage would be a similar size as Vornskrs in Star Wars, and Vornskrs are only 1x1.