Welcome to the Forum
Congrats on a great trailer.....
As you already have found out - there may be lots and lots of hidden repairs - depending on how far you want to go and how you plan on using the trailer.....
If you plan to tow a good bit, for a 30 plus year old trailer, prior to getting on the road, may I suggest you do a search on axles, the axle replacement procedure, and the importance of inspecting the entire interior floor/frame/shell interface. Unfortunately, a good inspection requires the dropping of the front and rear belly pans and the removal of a goodly amount of the interior. The point of looking at an axle replacement right now is that there is a definite economic benefit to ordering new hub and brake assemblies when replacing the axles as opposed to a total rebuild purchasing individual brake parts. There is no doubt that hydraulic discs are better than electric shoes, just be aware that there are options.
I surely do not mean to take away from your enthusiasm at this point, just pointing out some issues you may want to tackle sooner rather than later, especially if you are anticipating putting some big bucks and long hours into a 30 year old brake system.
Good luck on whatever course of action you take - the Forums are a wealth of information - take your time and take advantage of everyone who has gone before you down the treacherous road of rebuilding vintage Airstreams.
"Suck it up, spend the bucks, do it right the first time."
WBCCI # 1113
Trailer '78 31' Sovereign
Living Large at an Airstream Park on the Largest Lake Totally Contained in Texas
Texas Airstream Harbor, Inc.