1/32” will on the whole design itself when you scale from full size as the gauge/body proportions match, you will have to make some allowance for wheel standards being not quite to scale.
Now when it comes to 10mm scale you need to do a lot more engineering, as the frames are not to scale, it was done to give bigger boilers and larger outside cylinders (but is a bit of a pain for inside cylinder live steam locos) work out who’s bearings you intend to use, work back from the back to backs of the wheel set standards and build in a few thou of side play then you know your face to face dimensions of the frames, however if you designing a loco with a smoke box saddle or exposed frames above the foot plating this will need to be dummy as they will not line up with the actual working frames and will look wrong if you try.