Gmax is fine, how ever you will need the 3dsmax file exporter plugin since Gmax uses its very own file format.. kidna stupid i think.
Gmax has all teh features that max has that you need for low poly modeling. Never heard of Hash master...
Only jsut today I was teaching my friend how to do low poly modeling. We made quite a good head ^^...and a great model for his first attempt. I think hes getting the hang of it quite well.
optimising meshs is easy, just reavaluate the mesh regulary for areas that can or should be made simpler... search for vertexs or faces that dont realy need to be there, or areas that can be done by using less polygons than you currently have for that part. if it can be done by the texture... get rid of it, no need to model buttons, belt buckles and stuff liek that, unless ther overly important to teh design and look of teh model.