I have a Voightlander Avus that is very similar, they are a lot of fun to use. As to your questions.

1. You can certainly develop plus-X at home, if you do it in trays it will need to be completely dark. But Being that film packs were discontinued in the 80's I would not expect much from old film.
2. You are correct here just make sure you have the darkslide inserted in the filmpack before you take it off the camera, and make sure you remove it befor you make an exposure.
3. Can't help you here, I have never used a film pack. Did the camera come with individual film holders as well? This is how I use mine, I got 9x12 film from JandC (Efke 100) loaded in the holders and use as a small view camera.

They are fun to shoot with, additionally there were roll film backs that make them easier to use as well. Search eBay for Rada, Suydam, or Rollex(sp?), I have a Rada and it works great for 6x9.