you measure your body parts first against the size of the template measurement then using adobe/PDF file reader you adjust the %(e.g 90%), it really is trial and error! you print it out and fit the template to your body.(this is cheapest method as you dont waste foam). also remembering as you build you cheeck each part for clearance(so you can move/not rub etc). you may still need to cut angles/slices off because everybody has different size torso/limbs etc.
US use 'Kwickseal',i use foam putty for larger gaps,polyfilla flexible filler.
Mod Podge is ok for giving a hard smooth finish(you can make your own with PVA glue and water.I also use Hexflex(brush version of plasti dip)