I owned a 99 Beaver, as far as systems go, the heating system was far and away the biggest problem. What brand does this have in it? If its an Aquahot you should be alright. If its a Hurricane, plan on problems. I had the guts of mine changed, the controller changed, several new fuel nozzles, different exhaust and finally TWO different brand new boilers before finally getting it to work satisfactory. If you plan on using it in freezing weather, especially driving it, the heat exchangers were woefully inadequate. I added an additional high output multi speed heat exchanger and it worked pretty well. After finally getting the boiler issues worked out, I was able to comfortably use it in below zero weather.
Otherwise I was very impressed with the coach, they have arguably the finest cabinets in the business. The rest of the coach was pretty good quality, Beaver is a higher end brand, especially the Marquis. You will have minor problems, that's just the nature of any used coach, but at that price I think you are ahead of the game.
The Cat C-12 and the Allison transmission are both tried trued and proven. You shouldn't have any issues whatsoever than just regular maintenance.
Hope that helps, if it was me I would buy it. In fact if you don't, send me a private message with the details, I may purchase it myself.