Yes, that's the correct procedure, but, I've never tried an update like
that using `sysupgrade'--I generally do a fresh install from scratch.
I have used this procedure recently (with 10_BETA), and it worked flawlessly.
And, unless you're fine with compiling your applications from source, I
would hold off on the upgrade until the binary packages for 10.x arrive:
Technically, you can also stop after the kernel upgrade, continue
using a 9.x userland, and use binary packages compiled for NetBSD-9.
The kernel must be the same version or newer than the userland, but
nothing says they need to be exact matches.