Looks like a good start
However, i wouldn't trying to level the imperfections.
First, because the original helmets were full of them. Second, because i wouldn't try at all heating the helmet, it is extremely thin and warping risks are way too high, Third, because i think most of the imperfections are located on the areas which will be painted later on, and the paint will hide them for you; or located at the junctions between the face & back, which will mostly be covered by the ears.