Congrats on the new toy. You may not ever be able to find all the manuals, etc. for your rig. Fortunately, most RV's of this era were very similar in construction and sysytems. Unfortunately, they were in many ways inferior, sometimes frustratingly so, to anything made in the last ten years.
Take heart though, there is a ton of free info. here and on line. You can get one or two books, that show the systems, tips for repair, etc. (very cheap on Amazon, etc.) Big thing is go get the propane part of the system checked out by a pro. Then, if you can learn what you are doing, go over everything else with a fine tooth comb.
If you like to tinker, you will have a real good time bringing it back to life, so to speak. With some TLC and proper repairs if needed, your rig can be every bit as serviceable as a newer one and as fun too. For a lot less coin!
After 20 hrs. or so of research on RV's of this era in general, you will have a lot better handle on things and the confidence to fix that cieling and most anything else. The roof (exterior) might be a high priority...if the cieling is water damaged.
Have fun with it.
1984 Midas Freeport 24' Class C
Ford Chasis, 351W C6 @ 118K miles