So the PCBs arrived, and I assembled and tested one of the servo breakout boards. It's quite small, here's the comparison with a coin:
All the servo sockets (for those small, 3.3V servos) are on the back side:
There is also a voltage regulator there, and a couple of pullup resistors, and that's pretty much it. All pins except for the power are 1.27mm, to save space.