CHECKM8, there are a lot of tutorials around here, and you're highjacking a thread. Which isn't the end of the world, after all I've been parading my signature around like a banner and starting up side conversations left and right, but it's generally considered in poor taste.
To answer your questions, you want to use cardstock, anything under 110lbs is probably too light (if you can get something real heavy duty, like 160lbs, it'll stand up to resin better, but it might be a touch harder to work with, and your printer might not want to have a go at it).
Resin isn't particularly costly, I can almost guarantee a decent sized tin (liter or more) will run you less than $10, and I'll also be amazingly surprised if Home Depot doesn't have it, just ask someone. I haven't had to actually go out and buy any yet, as I have some laying around the garage.
If you have any more questions, I recommend the following tutorial pages, altogether they'll take you from scaling, through printing and folding, through resining and fiberglassing, and through finishing up with bondo:
http://www.405th.com/f19/complete-respirator-safety-guide-7550/
http://www.405th.com/f21/info-how-measure-size-your-pepakura-project-42098/
http://www.405th.com/f19/halogoddess-how-scale-more-tutorial-31627/
http://www.405th.com/f14/how-scale-your-armour-tutorial-v-2-a-25588/
http://www.405th.com/f21/faq-papercraft-pepakura-40607/
http://www.405th.com/f14/ultimate-pepakura-faq-3008/
http://www.405th.com/f14/tutorial-how-make-good-folds-pepakura-armor-1368/
http://www.405th.com/f19/crackhead09s-pepakura-tutorial-9454/
http://www.405th.com/f14/tutorial-pepakura-building-dummies-noobs-8791/
http://www.405th.com/f19/crackhead09s-fiberglassing-tutorial-9691/
http://www.405th.com/f14/resining-fibre-glassing-tutorial-how-1572/
http://www.405th.com/f14/pepakura-fiberglass-smoothing-tutorial-1525/
http://www.405th.com/f19/crackhead09s-body-filler-spot-putty-tutorial-9730/
http://www.405th.com/f14/tutorial-using-bondo-detailing-2814/
No. Seriously. There is a metric assload of information around here if you just do some looking. And yes, it's going to require a bit of reading, but I guarantee you that paying attention to resources like this are going to be the difference between a spectacular build and one that's utter ****e. The people who wrote these knew what they were doing, and the great builds you see around here knew to listen to those people. You have the opportunity to stand on the shoulders of giants if you're willing to do a little research and apply a little effort.
And
Alkatraz it's looking great. I like seeing people take on some of the less-common helmets, and EOD is definitely one of the more visually interesting ones. I look forward to seeing it finished. Personally, if I ever did a MJOLNIR build (and I just might some day, we'll see) I'd probably go with a JFO helmet.