Hi aaron,
One of the best tools at my disposal was two years of College classes in AutoCAD back in thee early 80's! With all the things I design and build, they have all had time in my computers!
With the large cubes, I drew a square, then drew a line connecting the points. then offset the lines .03125" to either side. then I deleted the line in the middle. This was done on both the top and side views. Now on the top view, I drew a circle .25" smaller than the square. With a depth that intersected the lines. then I repeated the processes until the center of the cube was reached!
By doing it this way, the points in the corners became equivalent to a 1/6" pin!
I hope this helps answer your 1st question. As for fixtures, there is no limit to the types and designs you can choose from. My fixture was an attempt to hold a rigid stainless cube, and it actually worked very well for the fragile Acrylic plastic cubes too (except for a little chatter in the surface finish!
Widgit