Well, the base is getting deeper every day. I've now reached what I'm going to consider to be the second tier of my base. It is 5 and a half blocks deeper than the first tier, and will NOT be using half slabs. While the final walls of my base (almost entirely glass) make the first tier difficult to light properly, I will not have problems at all with the second tier, allowing me to use grass (I love grass).
I decided on 5 and a half blocks deep because this allows me to put rooms underneath the first tier (or the top tier). I normally like rooms to be 4 blocks high. It doesn't feel uncomfortable or cramped, and the fifth block will allow me to create separate ceilings in the rooms. Or maybe that's an excuse, and I'm really just tired of digging out each layer that has a diameter of 82 blocks.
Originally, I wanted to stairs to be on one of the diagonals of the circle (since everything in Minecraft is a square, there ARE diagonals to a circle). In reality, when I tested it out, it looked awful. Maybe I'll change it later, but for now, this stair-style is what I'm going with.
The stairs and the half slabs I use for the first tier are still subject to change though! Stone slabs are nice and all, but I REALLY don't feel that they fit in here. Still, I would hate to use wood. It's a dilemma for another day.
As a fun side note: You guys should try and find my chests, then compare them to previous overview pictures and watch them grow from the overwhelming amount of dirt and cobblestone.