Hi PJ, we used to paddle on the fjords before they got rid of the ferry from the UK.
I'll try to answer your questions to the best of my knowledge, but also feel free to contact me with any other questions.
1. Boat rental. - I've never done this, but I've heard it is possible.
2. A Packboat would be fine, we used inflatables with no problem.
3. Not sure really, we got them online, can't remember where from, sorry.
4. Yes the official campsites are marked on the maps. Nearly every village has a campsite. Wild camping is also fine, as long as you are discreet. Everybody has the right to wild camp in Norway, as long as you observe a few rules.
There's only one problem with wildcamping in the fjords, the sides are bloody steep, lightweight hammocks are a good idea, unless you fancy sleeping in the boat! Wildcamping spots can be few & far between & they can be very popular during the holidays.
5. I've always buried human waste, but make sure its away from streams etc.
6. I drank straight out of small, fast streams, but if in doubt purify.
When are you planning to go? I've found it is dryer in June & July, than August & Early September.
You might live much further away from Norway than I do, but the silly thing is, its just as hard for us to get there, than it is for you.