I used Naraya’s female N7 armour template as the basis for my ME3 Ashley Williams armour, because its very similar to M2 Femshep’s. But I only took them as a rough guide, I imported files into corel photopaint (because that’s all I have), split he parts into individual objects(what photo paint call layers) and resized and redrew each part as I saw fit. I ended up with pretty much my own custom template in the end.
I think you have to take these templates as just a starting point, yes follow the sizing guide to begin with, but after then start measuring them and yourself and tweak and distort the individual pieces as you need. A lot of the bits of N7 armour are basically conical tubes, and you will have to adjust the lengths and widths at the top and the bottom to get a good fit to your body, not just the overall size.
I would suggest after you first round of adjustments that you print them off on cheap paper and then cut them out and tape them together (a lot of parts will be > 1 sheet of A4 paper) and try and wear them, hold thing them on with tape if you need, this is probably the best way to judge fit and size, (but remember to add a little to compensate for the width of the foam) , if they don’t fit, adjust again. I had to go through 2 to 4 iterations of each part on paper before I started cutting foam, and even after that I found some foam bits didn’t fit (as I said make allowances for foam width, oops) and had to resize and rebuild. Since there’s very little give or flex even in foam armour, it has to fit right or you won’t be able to move neve rmiond be comfortable.
Also have a think about exactly how you are going to assemble your suit, how are you holding it on to yourself, how are you going to get in it, are you going to have separate torso and abdomen or joined, how are you going to build around your shoes or boots etc etc etc and make adjustments to the design to suit.