I have a module with tiny castellations (half-vias) at 1.5 mm pitch. They are 0.8 mm wide and 0.6 mm deep. I am designing a breakout board for this - intended for hand soldering (not paste + pick n place).
I've seen breakouts for other castellated devices and soldered some myself.
What I am not really sure about is how long to make those pads - to make it (relatively) easy to solder.