*
Remember, I said DON'T use the mosquito repellent! Blowing it straight into you helm will make you sick!*
I made my helmet using Foam and pepakura plans adjusted for foam. I built it with about 3/4 inches space on each side of my head and now I'm putting in 1 inch foam from a Jo-Ann Fabrics, and actually using fabric glue to glue a comfortable black fabric over it (I don't know how to sew).
Wires can be controlled with putting them into "conduits" in you undersuit. I got a morphsuit and plan to glue (or sew) on anchor points (maybe even spandex fabric tunnels) to keep them in place (just plan for how much your undersuit will stretch). *But, all this is experimental, so it might not work.*
I found some fans that are like miniature blowers, so they can work inside the helmet attached to the side, but they have been discontinued.
Like an "Antec Cyclone Blower " only smaller.
(
http://www.newegg.com/Product/Product.aspx?Item=9SIA24G28M7085&cm_re=blower-_-35-209-052-_-Product)
(hope 405th doesn't mind me posting vendors references here, I didn't read the posting rules yet).
The Antec Cyclone Blower can be put under your Armor, and blow thru a flexible fabric tube you can make to cool you. Just sew or glue a "D" shaped tube of fabric (PET foam ridges can be glued inside to keep the tube from collapsing completely) that fits the fan. Spray the tube with Plasti-Dip to make it air-tight (don't get any on the fan). The flat side sits against your body, and can be Velcro-ed into place. Just point it into the base of your helmet to help cool it.
Good luck on the armor!
I've been trying for 8 years to build mine (3 different tries: 2x Mk5's, and now Mk6). It's hard work.