Thank you for your detailed instructions!
What exactly do you mean by a foundation, and what is the point of one? Do you just mean what will be the floor, or something different?
I have heard of megaprims and think I have a free set of them but I have not worked with them before. Are there any details I should know to work with them?
I like the idea of making the edges of walls transparent, because I tried making a house today and the fact that I could see the "seams" between pieces bothered me.