I received only Japanese documentation and I don't know if English versions exist. I was bothered by that at first, but I spent a little time with it and became comfortable with everything.
I don't believe there's much unique about caring for the Nexus housing. It has only two retaining clips, so try to open them both together to avoid stressing the backpiece. They provide their own o-ring grease, so whatever o-ring maintenance program you subscribe to is valid.
Setting everything up requires a little patience. The lens rings and gears will have english docs so follow those. Put the extra rubber pieces in your camera kit in case you need to make adjustments on a trip. Setting up the multiport takes a little time. First you need to adjust the base so that it aligns on the housing properly. There are alignment dots to help with that. The flat ports need no alignment. If you are getting a dome with the multiport, you align that next. Then you align the extension rings. Plan on spending an evening testing each port and lens combination to make sure everything lines up. When aligning the ports, make them pretty tight so they don't risk loosening on their own. Don't go so tight that you can remove them later! My camera just dropped in and worked perfectly. You will need to remove the rubber eyepiece, install the magnifier, and focus the VF diopter. There's also a ring the installs on the function knob. That's pretty much it.
Specific to the D100, you must use a dual sync cord and connect it to a specific bulkhead (secondary, I believe). The reason for this is that Nexus includes a "smart" strobe adapter that has little LED's that indicate recharge. This adapter is not fully functional with the D100 and one of the bulkheads can't be used. Hopefully they will fix it or offer a "dumb" hotshoe adapter as a downgrade. This is not really a problem. Take a spare dual sync cord, and if a bulkhead fails, switch to the other AND internally exchange the wiring. I prefer single sync cords, but this is a minor gotcha.
All my controls worked beautifully at first. After two dives, one control stopped working and I couldn't for the life of me explain it. As far as I can tell, it was impossible that it moved or failed, and I think it was just a freak thing. The only other issue I had was with the shutter lever. It's return is slightly soft underwater and has a tendency to not release completely. If you get no image preview and no "remaining shots" indicator in the window, push the shutter lever to fully release it. It won't move noticably, but your image preview will jump on the screen. Again, it's not a problem unless you don't realize it and get no previews underwater like I did most of the week! I expect this problem to disappear as the control breaks in.
Since you are nearly there, I hope you consider the 70-180 macro. It is big, heavy, expensive, and makes changing the camera battery a chore, but it is glorious underwater! Once I tried it I had no interest in the 60 or the 105. Rumor has it that the lens has been discontinued so they may become hard to find. The WP-4 dome works very well with the 105 and makes the lens easier to frame with.
I know you are going to love your Nexus D100. I now have five divers in my immediate group who plan to purchase one. Two have placed orders already.