My personal opinion is this:
If you're running just one disk (ssd/platter, whatever), then forget about partitioning.
Partitioning is ONLY important when you spread data across disks (again, I mean SSDs as well, even USB flash drives).
Let me explain. Suppose you have two SSDs. One could have root and var and tmp. The other, presuming you build a lot of packages, could have usr and home. That way, it uses tmp on one disk and usr on the other when building packages. This is just a simplified example.
Years ago we used to partition disks to use the closest to the parked heads for quick access to the most used data. That was so long ago and is no longer relevant. It's especially irrelevant for SSDs as it's just circuitry.
So, forget all the effort of devising partition plans and just make the entire disk NetBSD. Then you're not stuck to fixed sizes.
One thing I would do is not use the entire SSD. Most manufacturers suggest leaving 5-10% free for wear leveling.
(this depends on your manufacturer)