If you're new to pepakura, I'd recommend starting with one of the simpler pieces rather than the helmet. The helmet may be the most iconic, but there are a lot of components to your armor that will go together a lot more quickly and provide lots of practice to hone your process and skills.
Also, unless it's a super-huge build (25+ pages), I like to tun on the tab numbering and do my stuff in stages, especially if it's a build over a very long period of time like this. Cut everything out,
then score all the pieces, and
then finally build it. This doesn't always work well for some of the largest pieces, but it works well for most builds, and it's hard to crush flat pieces of paper before they're glued together. I'd also recommend keeping everything from one piece together in a flat box or folder until the actual time to glue it together comes. That way, your pieces are less likely to be lost or damaged before you put your piece together. I'd also recommend roping off (metaphorically) a section of shelving or workbench to store your build when the time comes to actually glue it together. A dedicated space for your project, out of the reach of pets and children, can help keep your project from getting crushed.
For the actual construction, I agree with the recommendations from
Lt Shiny Sides and
PerniciousDuke to use an Xacto. You can make some very precise and clean cuts with one when paired with a METAL ruler. Do
NOT use a plastic one unless you really want a ruined ruler and plastic shavings everywhere. Then I have wonder why you're such an odd duck.
A high quality sharpener will also go a long way and save on replacement blades, whether a pep or foam build, and as counter-intuitive as it sounds, a sharp blade is a much safer than a dull blade.
During actual construction, avoid hot glue. This can work for foam, but it's a nightmare when trying to get clean seams on a pep build. I know a lot of people recommend super glue, but I prefer to use one of the faster drying Aleene's Tacky Glue, either Quick Dry or Turbo, on my cardstock. They allow a little more play to line up seams, and holds position on all but the tightest corners in about 10-15 seconds. And remember that less is more. Globbing it on will only make it messier and increase drying time. A thin, even layer is all you need.
And never underestimate reinforcements and support struts. Many of the bigger builds already have them worked into the pep file, but some of the smaller ones don't. Take the time to create and install some reinforcements in your piece. It can be as simple as a piece of cardstock glued to the back of a larger face or popsicle sticks used to hold angled openings. There's nothing worse than watching all your hard work get warped and having to start all over again.
For motivation, normally I'd recommend taking a break, but on such a long term build like this one, I again recommend working on on of the smaller pieces. It's frustrating when you've worked on something for months and have nothing to show for it, especially after it gets ruined. Working on one of the smaller pieces and having something to show in a week or two can be a nice reminder that what you're trying to do is not impossible. It just takes some time.
