nice graphic...but why make a massive mob trap? Sounds like a lot of extra work for not a lot of materials gained. A simple fire pit in front of your house, pressure plates with tnt under them, or arrow dispensers would work just fine as mob traps.
You get like 10x more from a large mob trap. You also avoid getting hurt and having to reset the traps. And I honestly didn't think of it as work. It was pretty fun for me... although the mining got a bit much at times. Edit: Some things I should have changed/added: -It's a 2x2 hole in the middle, not 4x4 -Make sure to light up all the surrounding caves/coastline. That's a huge step I hadn't thought about