Hi, ledow, welcome to the forums!
The Mini does indeed have a 16-bit framebuffer. The only Kobo models with a 4 or 8-bit framebuffer are the original Kobo and the Wifi. The Touch, Mini, Glo, and Aura are all 16-bit.
For updating the e-ink display after you've written to it, you can check out my code
from here and also tonyv's code
here.
SDL can write directly to the Kobo's framebuffer no problem. I've used pygame, a SDL wrapper for python, to draw to the screen. I also managed to get SDL gnuboy to run on my Glo, although with no keyboard there was no way to control it.
Hopefully this is a little helpful, if you have more questions feel free to ask away.