I have been printing in PETG for years with lesser printers so this is a piece of cake for me. Literally the first printer I've never had to tinker with.
Thanks to you, I knew to check the scaling and they definitely haven't fixed it. I brought the parts into the 3D Builder program in Windows and lined them up. I scaled the chest down to 98% and they lined up pretty close, so I think that's about the sweet spot. Might need to grind down where the arm hole edges don't seem to line up.
I'm definitely going to attempt magnets for lining parts up the chest and back. I never trust 3d printed interlocking to hold permanently.
For attaching the panels, I'm going all out. CA, then welding with a 3d printing pen at the seams and/or soldering iron, then using a hot stapler for a physical bond.