I may be repeating a few things other people have said but I am just throwing my tow bits in...
1) foam is usually more readily accessible, cheaper to use, flexible and forgiving, and lightweight. It is a great way to start out, and can be somewhat easier/faster to work with. If you mess up you can always quickly make a new peice. The only downside is after some time with folding and wear, the foam will crease and wrinkle. This can be prevented and solved with different methods, but can get somewhat pricey. Not by too much though. Pepakura(using paper) is easier to get the shape you want because it forms into the design automatically, where foam you have to cut at the right angle and glue perfectly. The pepakura part gets messy and can be expensive and VERY time consuming. People will say that it gives you better detail than foam, but it all depends on how picky you get. I have seen pepakura projects that are unworldly good, and I have seen foam projects that turn out better. It just depends on how determined and picky you are.
2) it is relatively the same, but you do have to cut the edges at an angle depending on how the peicesalign, and you also have to account for the thickness of the foam.
3)there are many different options. I have seen great visors using a variety of methods. I made mine out of plexiglas glass and window tint. This is a great and cheap way to do it if your visor isnt a complex shape with many bends and contours. You can also use motercycle helmet visors you find at the thrift store, plastic from a two liter soda bottle, vacuum form a buck and dye the plastic, colored sheet dividers for three ringed binders, buy custom ones online, and many more. This depends on how much you would like to spend, the resources you have, and how good you would like the visor to look. For EOD helmets, I reccomend finding a cheap pair of sun glasses with fancy metalic lenses in the color you want, pop them out, and use those.
4)you will ultimately have to scale the armor to you. You can do this a few ways like inside the pepakura program by using a measuring tape on yourself and inputting the size, or purchasing the armorsmith program to make a digital mannequin of yourself. Size doesnt matter at all! I am 6'4" but maybe two inches taller in my suit. I am a little bit taller than those in the suits around me so it is sometimes funny, but most people are in the same boat as you *cough cough* Canada *cough*. Theworldstallestspartan is 7'2" and is the same height as cheif in and out ofarmor, and there are plenty of Spartans that are shorter. Noone cares, because it is fun and we all, and you will too, look amazing anyways!
5)again, it depends on what you want to do and how detailed it gets. My foam suit cost $200 to make, and most of the cost was glues, paints, and other items that wasnt the materials itself. If pepakura, the fibreglass and resins, plus bondo may make it a little more expensive. If you want to add LED lights and fans, or even speakers and audio emitters, this also adds up the price. I would say your build would cost no more that $300 over time, but it also may be more if you dont have a heatgun, dremel, bandsaw, or any tools, but these are by no means necessary. Time wise, you could build it in less than a couple months if you were putting in many hours a day every day, or it could take you half a year if you are taking your time to make it perfect and are making an effort to get as much detail as possible. It took me three years to do mine, but that is because I procrastinated for about two years and seven months worth of time instead of just working on it :b
Wow this is a very long post... I wish you well on your journey, and if you have any questions, feel free to ask. Welcome to the 405th.
P.s. I cannot reccomend this more that you read and do as much research as you can. Look at other and similar builds to get ideas, and post your progress so we can all marvel at your hard work and give any advice if needed