>  What models of MIPS-based NeWS hardware do we support?

NWS-3410 and NWS-3470 should work.  NWS-37xx may work, but untested.
NWS-38xx does NOT work.

>  What is the usual process for installing NetBSD/newsmips?  I have the

Perhaps installing on NEWS-OS is the easiest way.  Prepare another disk,
extract binaries, installboot, and ln netbsd vmunix.

BTW, the machine name is not "NeWS" but "NEWS".  This is not a window system.
:-)