Treefarm 2.0 is open for business!
2 levels of oak, 2 birch, 3 spruce (since spruce needed to be 2 blocks away from one another) and 4 2x2 dirt areas on the inside to plant giant jungle trees.
I ended up only adding 1 additional level from the original design and tweaked the width of the levels a bit. If we find that we need to add another oak level or something it's easy enough to do.