im pretty sure your speedo problem has to do with the speedo pickup. it in the differential, and its a 2 wire lead with a L shaped boot that connects to the pumpkin.
the sunroof - on the rear of the roof there is a drip tray. if its not in place, it may be in the roof itself, where the panel slides in. the difficulty in opening may be due to the fact that it needs adjustment, or lubrication.
for the power windows, i would pop off the door card and test to make sure that there is current going to the leads that go to the windows motors. thats a good starting point.
you can find door handles at online stores like bavauto.com, pelicanparts.com, maybe even bmpdesign.com (not likely) or autohausaz.com. or you can check a local dump to see if they have another E30 there and lift it off that.
your other probs would just be guessing on my part, but good luck, and welcome to ub and E30 ownership!