The special bolts arrived this weekend, and I got to try them:

The good things about them: they are exactly the right size of the micro:bit's holes, they are made specially for soldering onto the PCB, they have this small pilot nub in the center, that lets you give them an exact position. The bad things: you have to be careful to make them exactly vertical, or the micro:bit won't fit on them, the standard nuts are too big and short neighboring pins (I need to find some kind of washers for them), they take somewhat long to heat up enough to melt the solder.

In other news, I'm still struggling with getting the screen to work. I might switch to a ready module at some point.