Designing a PCB for a Gamepad rev1

I have a vague plan on making my own Raspberry Pi compute module powered handheld gaming device but I don't know anything about designing PCBs. To learn how to create a PCB I decided to start small. Really small. I decided to make a gamepad with just 11 buttons and some header pins for an Arduino Nano.

I chose Kicad for my CAD suite because I've heard good things about it and its free. It did the job well enough and I will probably continue to use it for at least a couple more projects.

Mistakes where made but I learned a lot about the process and now I see many ways I can improve and expand on my design. Success! Can you spot any problems with the board bellow?

An image of the gamepad PCB with an Arduino Nano inserted in the header pins. Image of the back of the PCB showing the substrate with no solder mask. The copper traces on the front can be seen through the substrate.

Fixing some of the problems with it

Expanding on the current design