I've always wanted the gi joe flag, that thing is huge. As far as my favorite toy it would have to be my Captian Gloval GI Joe custom, it was my first custom. I would also try to grab my soul of Chogokin Getter Robo G, Liger, and posiedon.
The legs do look short. Another idea to make them larger would be to saw them in 1 or 2 sections and add styrene strips in between each section. After that you might have to split the legs down the center and add a strip or two a s well. You'll also have to do some shaping with putty. I would do the same to the thighs and feet. It looks like it's coming along, keep posting pics.
Looks like a nice project. If he is able to scale the dimensions and dynamics correctly that thing will look way better than the matchbox version. I've been working on a similar custom myself. You should put this in the how to cusomize section.
Just stick to Bandai, Yamato, and Takatoku. These companies provide excellent quality toys. I only make exceptions for other companies when the toys are rare or were never made by anyone else.
When I putty something I put it outside and let it dry completely or overnight. The smell will be alot less when I sand it. The only problem with that is projects take forever to finish. Besides the glues, I think accelerators like zip kicker smell even worst.
I've used Tamiya acrylic paints on some difficult vinyl like plastics and I never had any problems with them. Although, I prefer Testors regular paints or Model Master series, they have always worked well for me. As long as you sand the plastic well the paint should stick.
Late reply, but I've had the same problem with a few things I've painted in the past too. This usually happens more so when you clear white, after time the clear may yellow. Factors include if you touch paint with your fingers. The oils in your hands can affect the paint. Also, applying polish can yellow clear or white paint. Even if you keep the item out of the sun it can still yellow. Both plastic and paint are delicate and must be cared for. You can repaint the valk if it gets really bad or let mother nature take its course.