Fantastic work! What I really appreciate out, is that you can visually see from the quality photos that you took your time. Thats honestly the most important part of any costume you see someone make. Your cuts are emaculate, even your bevels on the breastplate which I remember being SUCH a pain when I first did the DFT suit.
I have a few tips for you! I saw you were thinking of using a trashcan for the backpack, and I love the idea! Even better, is most store bought items like that list the primary material that they are made of. My holy grail is to use "This to That." It's a website your can find on a simple search to determine what adhesives work best with what materials. PPE as always is a must!
Second, as daunting as Pepakura is, treat it like you are learning to ride a bike. Make mistakes with it. Scale something that could fit your neighbors cat or cover your TV. I also highly advise using your budget the purchase the full program. It might cost a bit off the bat, but you are then able to save the files you alter for future reference or even altering further. Its indisposable. I know a lot of people recommend Armorsmith nowadays but the versatility of Pep vs Smith is unquestionably beaten out.
I also highly recommend even just investing into a resin helmet. Helmets can be a immense pain to scale as I previously mentioned; and getting a helmet teaches you the basics of working on a cast piece. Usually as well, a supplier also offers the visor that fits their bucket perfectly! I really learned my painting technique on casted products because its such a focal point that you slow down and learn what works for you and what doesn't.
Final tip alongside painting. Take your time with it. Walk around in the armor, imagine what kind of environment your character is. Muddy? Rocky? Sandy? It'll leave different wear across the armor. Scratches should be prevelant but not overbearing to the overall piece. And use multiple shades of colors to achieve shadows to lighten or darken your flat zones! And make sure finally to heat seal all that pretty armor before applying plasti or whatever you choose to seal it. (Though you can always choose not to seal! Foam will just absorb more paint which means using up more of that budget you mentioned)
