First, welcome to the board. We have a lot of fun here so I am glad you have joined us.
Of the two arrangements, I think the "checkerboard" one is more interesting and would look very good. You could also really mix them up randomly.
I don't think you need to do any sashing on this project. If your fabrics were busy prints sashing would probably be needed but with the fabrics you are using...not necessary at all.
Keep going...you're doing fine.