well there is no fixed size on this id say, as we need to resize it for anyone seperately
what i can tell you is, that RDJ is 173 cm in height, so the movie suit will be modeled to his size specifically. given that the helmet adds maybe 2 cm, and also maybe 1-2cm on the soles, rounded up, id say 180 cm is a pretty good height for the iron man suit. apply that on
also i dont see any need for a new helmet pep for now, as it hasnt changed a lot. the details will be done in the final works of bondo etc anyway