Correct on the first two points.
What's confusing me is that when I create a vDS I'm asked how many uplink ports I need and underneath it says 'Maximum number of physical adapters per host'. Are these supposed to be one and the same thing?
They are not. You can have 12 NICs in a box but only allow 4 of them to connect to the dvSwitch via uplink ports. The number of uplink ports determines the max number of physical NICs you could use.