Dude, very nice work!
I'm printing the same files as you are, and settled on the same armor clamshell and buckle setup, but figured I'd add some "locators" (basically blocks that can be epoxied in, one with a hole and one with a peg) to hopefully keep the chest armor sections from shifting. I haven't tried them yet (fiberglass for armor reinforcement arrives tomorrow), but I'm happy to share the (incredibly simple) design if you're interested.
I'm wondering how you made sure the arm and leg armor stays in place though. More buckles sewn to the undersuit?