Goal was a small driver board which only need power supply and I2C and then drives 16 motors at once. In several iterations we found out that the best way was to have all I/O pins on one side, both for size and later wiring. Furthermore, having two pins (one on each side of the board) drastically reduces complexity of wiring and faults compared to the first intended common ground wire, where all motors share one wire.
A variable voltage converter can supply the board with the 3.3V necessary for the here used vibration motors, and can be supplied e.g. a normal 5V power bank. Since the regulator is directly on board of the driver board, the system is scalable to even bigger (or smaller) vibration motor arrays. Board layout and 3D-design files can be found here.