I figured that my design was pretty much as done as I could make it, so I posted it on /r/PrintedCircuitBoard to see about getting some feedback. As always, the electronics subreddits tend to be quite wholesome and education, and full of supportive people willing to help out. Thankfully, they gave me a lot of good feedback, as you can see below:
I was happy to learn that KiCAD automatically takes thermal relief for pads into account, as before this thread I had no idea what this was. The other major thing I learned was that there is no reason not to increase trace thickness if you can. And, finally, I learned that there was such a thing as a decoupling capacitor to smoothe out power delivery to a microcontroller, and so I added one (and after advice moved it closed to the microcontroller). That all resulted in a slightly changed design. Furthermore, I solved my issue with the footprints by simply taking a digikey footprint directly from a component I am intending to buy, so that the problem solves itself. I am very excited to come to a close to this project, and seeing it in action!