I use Eagle. I consider it easy to learn. If you are starting from scratch then spend 30 minutes looking at KiCad too.
That seems like a lot for that size board. That is just one PCB? You may need 4 layers and that is a tough place to start. Maybe just start with 2 or 3 things with the Teensy. The boards are so cheap that you will only spend $20 and a couple of weeks to fix your first 5 screwups.