Awesome work so far! Your garments look great. I made a kabuto, do, sode, and kusazuri a few years back for a Samurai Avengers cosplay. I think it turned out okay, but it definitely took more time than I anticipated, so I couldn't get the entire thing together before the deadline.... if I recall correctly, it took me about 30 hours just to lace the things together! Because of my time constraints, I ended up just buying a karate uniform to wear underneath. It worked well enough for my purposes (haha).
I used the same website that you've already mentioned and found that those patterns translate very well to sintra. The sintra is easy enough to form with a heat gun, but be aware that it does not take extreme curves very well, and it will snap if you push it too hard. Also, it's a pain and it takes forever, but adding the reinforced "stitching" under the laces to hold the panels together is very much worth it. I used some thin wire and covered the ends in hot glue on the backside so they wouldn't catch my clothing underneath.
I hope you enjoy the journey!