I prefer to set the shower pan first, and then run the flooring up to it.
This way you can shim if needed, and it doesn't show a gap at the front.
The flooring will cover any gaps.
You have to set the pan level, but the floor may be anything but level.
Never assume an old home has level floors.
That also means that when you step from the floor to the pan, the height is closer.
If you set the pan on the finished floor, you will be stepping up.
Setting the vanity first or second, you can make an argument either way.