To me that means you only smell it before the cat converter warms up.
This is normal.
True, but it can happen. There is some sort of boot or gasket on the firewall, where the steering shaft goes through. Twice on my Chrysler minivans the bellows on this thing has split, letting in some sound and, if present, some smell.
Check that and all grommets, etc. on the firewall.
Varies car to car. What type of transmission fluid is recommended in the owner’s manual?
I’ll guess that the owner’s manual states to use Nissan CVT fluid in the transmission, not hypoid gear oil.