I tried to watch Xorg.*.log with an ssh session.
What happens is interesting: for the 45s that it takes startx to do its thing all ssh console communication is blocked. When terminating X11 the console through ssh is unresponsive for a few seconds, too.
Needless to say that I didn't learn much more ;-)
Maybe I should try using a different machine to install #NetBSD on, and if only to learn what's normal and what's not.