I think the banned guy had sourced those lights as 12-volt car leds or something didn't he? I'd have to go back through the thread to be sure. I'm pretty sure from the endless jokes Craig made, the real Geoff could go more than 12ft from a wall outlet, so you are close to being spot-on with 120-volt versions of the eye-leds. And there's always the option of an extension cord.
As for the mohawk, instead of metal I had thought of trying to find an appropriate thickness of sheet Styrene and and making it out of that, simulating the welding of the mohawk to the curving base that attaches it to the skull with some gooped on resin or maybe melted Styrene sculpted to look like welds and paint the whole thing with paint until I achieved a metallic look.
As for matching the look of him, it would probably be better if references photos of him could be obtained rather than trying to wing it from screen-grabs off tv. It's a mystery where Geoff wound up as far as I know. Maybe Ferguson has him parked in a corner in his house? If all else fails the one person I can think to ask is Josh Robert Thompson who voiced him who has a presence on Facebook and interacts with fans. I sense that he's beside himself with fans who keep clamoring for more Geoff Peterson because he's trying to be known for more than just Geoff, so asking him about it the wrong way would be like asking say William Shatner or Leonard Nimoy about Star Trek in 1970 when they too were desperate to move on to something else in their careers.
Other than that, asking Grant too might work. Geoff's 'mortal remains' might have been shipped back to him.
I look forward to seeing how you do on your Geoff Neil. If you start a separate thread for your build, please post the link here. I think you've got all the elements of an excellent start there.
