Yes, setting the layout will consist of something similar to this.
"cols": [0.0, 1.0],
"rows": [0.0, 1.0],
"cells": [0, 0, 1, 1]]
The cols, rows, and cells define what the window will look like. I haven't done much with layouts before, so I can't help you much there. The *.sublime-settings files store settings relevant to a given plugin. You specify the name of this plugin when you run sublime#load_settings. I'll see if I can come up with some additional plugins that may help you. Feel free to ask more questions. There are no notifications on this forum, so you may also want to try posting on stack overflow. I know there are a handful of ST plugin developers who watch those tags.
If you haven't already, you msay want to take a look at code.tutsplus.com/tutorials/how- ... -net-22685. While it doesn't cover everything, it's not a bad starting place for getting acquainted with ST plugins. As that tutorial was written for ST2, it may not work in ST3. If that's the case, you can grab a version of ST2 to go through the tutorial, or try to figure it out yourself. There aren't many changes between ST2 and ST3, but those are relatively easy to explain if you are familiar with ST2 plugins.