The Golden fullmoon maple generally gets quite a bit wider than tall. I would allow for at least a 15' canopy spread (more if possible) although it will take some time to get there starting with a 3' tree!! So that means space it about 8-10' away from the hemlock.

Thanks a lot gardengal... I considered about 6' from the trunk of the hemlock. but I think giving the maple a little more space will be much better in the long run. I want to avoid having to limb up the hemlock as long as I can, though eventually it will happen. I think 8' will be the magic number/distance. Thanks again!