Very interesting and a lot of good detail. Unfortunately you are lacking a very central detail: The podocytes. You seem to have used the old theory that the filtration mechanism is actually the basement membrane. It is not. The estimated pore size of the collagen network in the densa layer is 15-25 nm (different references give different figures in this range) which is way to0 big to give the experimental 7 nm cut-off. The actual filtration mechanism is a comb of nephrin molecules bridging the foot processes of the podocytes. These wrap around the glomerulus capillaries. As a comfort I can say you are not alone in this misunderstanding since this was the understanding until around year 2000 or so.