Hi Dave and Welcome to the Forum!
As far as the appliances and systems, get a flashlight and notepad and find the ID tag on each unit. Write down the model and serial numbers and this web site will get you started:
Service Documents and Manuals
Start Googling the rest as Mike suggests.
As for switches and such that are more specific to the coach builder you'll probably have to resort to trial & error. I believe the Covington was made by Firan which made a good coach but I doubt there is anything special or unusual compared to other models of that era. Maybe someone will cough up a manual for you but most RV Owner's Manuals are very generic and cover several or even all the models they produced.
Best of luck and have fun with your new motorhome!