I just went through this a few days ago, so here's what I figured
out:

Mouse problem:
Use "wsmouse" for the protocol.
Use "/dev/wsmouse0" for the device.  For some reason "/dev/wsmouse"
doesn't work.

Blank screen after exit:
It's not actually blank, just very dark grey on black...
(Same difference, right?)
For some reason the color map is not restored when you exit.
I don't have a fix other than "turn the brightness on your
monitor way up until you get X working"...
From what I understand, it's actually the responsibility of
the X server to do that, so its not a NetBSD problem.

Shared object "libXaw.so.7" not found:
Just make a link to libXaw.so.7.0, and then repeat the
same process for all the other libraries that it complains about.
I had to do this for just about all the X
libraries, and then everything seems to be fine.

   -Jeff