I have the Super 23 and have two lenses: 100mm and 65mm. They both are great lenses, but I don't know all their functionality with the Universal. So if you get a second lens be sure it will work on the Universal. I had mine out today: focus, wind, set shutter, set f stop, remove dark slide, and have a meter. It is a heavy rig and not for the rapid fire types.
I re-did the seals on my backs with a kit from someone in Japan. They fit and were relatively easy to install. One of my backs didn't work at first but I was able to fix it by bending a small metal part.
Besides the weight the biggest problem is remembering the list of things to do before shooting that I listed above.
Here are some of my less than inspiring images for my 23: