I did not read anything after the first page so someone probelly said this. But when I make getto-fab figures adn stuff I use balsa foam or clay, I have acsess to a FDM modler so I will try tahtn when I get around to it. and then make a trail mold from plaster of paris, then bondo if it all gose well. use murphys oil for a mold relaise. If you want to make stuff out of pro materials then Smooth-on sells everything you need. And they will sell small quantitys of stuff too, witch is nice from a commercail company to do that.
When you cast whatever you are casting i do it like you would chocolate. Fill the mold spin it around to remove air, then wait alittle bit then pour it out. repete it until your happy. you can also do it in a slip casting style, fill it up then wait un till the wall thickness has devloped then pour out exsess. hope that helps