I am most puzzled about the car rolling freely when in any gear. It should not do that. Even a badly worn clutch will slip, but there should be some resistance. (My experience was burning out the clutch in an Audi A6, the clutch would slip - the engine revolutions would shoot up rapidly without corresponding car movement - under hard acceleration. It sounds like the clutch is not engaging at all. Why is the question. Mechanically, when you depress the clutch pedal it should move the release or throw-out bearing which pushes the clutch plate away from the flywheel. This disengages the clutch plate so you can shift gears. It sounds like the throw out bearing is stuck so that the clutch plate is unable to contact the flywheel. Or maybe the hydraulic portion is empty or failed. You will need to [carefully] get under the car and check out the mechanical and hydraulic linkages to make sure they are properly connected and if they operate. I cannot tell you if it is possible to view the clutch/flywheel assembly because I have never disassembled them, but someone on the forum may be able to answer.

I assume when you turned the rear wheel, you had the car jacked so both wheels were off the ground. These cars do not have a positraction - the wheels are not connected in the differential. I think that is what you mean by the "differential being free". As long as both rear wheels turn independently, it sounds like your rear end is ok.

Finding windshield trim pieces is a problem here, too. Generally you have to buy them from either a car being "parted out" or a junkyard. I think I saw a recent post in this forum about a car being parted - do a search and contact the poster.

You should verify this answer by a search on this forum, but I believe the trunk lock operates via a vacuum line. It is possible the line is disconnected or has a hole in it.

You should download the service manual. Again, by searching this forum you should be able to find a link. It might be in one of the sticky notes at the top of the forum topics. It's a 82Mb pdf file with lots of technical information.