I would stick with just one layer, as the food really needs to be changed daily. When it comes to quantity, I use little plastic tubs a little bigger then you average kritter keeper, and I split up a 600 worm cup into two containers.
BTW, glad to see someone feeding their BSFL. Too many people stop feeding BSFL to their adult lizards, due to their small size, but BSFL typically have completely empty guts when they are sent to you,as they have nothing to eat in their little containers. A little feeding goes a long way, not only do they get long, they plump up too!