Like Red says, a lot has to do with your trailer's condition and what you want to do with it. If you know you are going to do the full Monty, then your path is much simpler. On the other hand, if you want to make it usable with reasonable cost, then you should develop a plan of action. I bought a 31' Sovereign
in January and just finished it this month. I'm retired so I could work on it at will. Here are my suggestions from my experience. By the way, Panama Red's thread was invaluable in my experience. Particularly his Vistas 101 part of his thread.
In addition to finding and fixing other leaks, if the gaskets on your vents on the roof for your sewer haven't been replaced in the past 3-4 years, they probably need it. They are a big source of leaks and floor rot.
If you haven't already done so, check your floor out thoroughly. An AS this old will probably have some floor rot and if you don't check it out first, then you can invest a lot of money and time only to find out you have big floor problems. Check threads on here for info concerning rear end separation and rear end droop. They can both be big expensive problems.
Another very important item is to check your axles to make sure they don't need replacing. An AS this old will need new axles if they haven't been replaced in the recent past. Threads on here will help you determine if you need them and where to get them.
Floor rot and axle replacement are the big items you need to know about before you invest too much time and money because they are essential items in a successful rehabilitation of an AS in my opinion.