If I were you, I would get the Nikkor AF-D 24mm f/2.8. It's $265 for EX condition on KEH, lightweight, will autofocus with your F5, and 24mm tends to offend fewer people than 20mm, so it's likely that you will like it as well. But of course it's your choice.
If a good zoom is not on you list, you should buy the 24 mm lens before the 20 mm lens. The 20 mm lens is more specialized ==> example making an object in the foreground dominant. The 24 mm lens is, at least for me, more useful ===> street photography, traveling and removing power lines from the composition of an architectural photograph of a building.
Warning!! Handling a Hasselblad can be harmful to your financial well being!
Nothing beats a great piece of glass!
I leave the digital work for the urologists and proctologists.