Your blocks are georgeous!! As to sashing size, I think that is kind of a personal choice. After you get a few more blocks made, you could lay them out on a sheet or a yard or so of your sashing fabric, if you have that much, and space them 1" apart, then 1 1/2" apart and so on until you are pleased with the way it looks. It also can depend on the finished size you want your quilt to be, or in your case the size of the top of the bed the quilt is going on. Please post pictures when you finish. Again, your block are very interesting.