Hey Steve,
You could also look at the Egyptian line of molds. Ima and I have both made stuff that is Sci-fi based with those molds. Also it depends on what area of SW that you want to build for your kids, or they build. The Sci-fi molds are excellent place to start and can be used to create different areas of the SW universe. You could do some of the tattoine builds using foamboard, then add detail pieces to it, then cover with drywall spackle. B2Martian has done that, here is the link http://hirstarts.yuku.com/topic/3306 to at least one of his topics. http://hirstarts.yuku.com/topic/1585 is his other one.
Here is one thing that I have done with the Egyptian line of molds mixed with the Sci-fi molds.
http://www.voidgamers.com/channel/HADD9/b.396.r.449.html

About the minis go to the nearest gaming store and see if they wont cut you a deal if you buy some of the common minis in bulk. Some places are great especially if you tell them that you will see them next week. A returning customer is always better than a one time customer, imho.

Hope this helps.
Duke