I was thinking about sculpting the whole thing in wax but then I didn't want to have to do a brush on mold... materials I don't have at home, so I'm covering the wax with a layer of putty
You can use whatever putty you want, I'm using the same stuff that I used for my 1/60 figures, which is really meant for miniatures but I'll stick with it. People usually use milliput, kneadtite, plumbers putty or that crazy bondo stuff (nasty dangerous fumes). If you want something non-toxic, try something called apoxie. I like using wax because it's reusable. I no longer work with sculpey because I hate having to heat it and it usually cracks. People love it though.
Geez, that left leg is so off... gotta fix that...