Welcome to the forum and the madness of vintage motorhome ownership.
Drop on over to the motorhome corner of this place and dig in, lots of info to be found there. And a number of helpful, hands on owners, who can usually answer any questions that may come up.
Sounds like you may have found a gem there. One owner, mostly original. That is a big plus, as sorting thru the changes have happened to these old coaches thru the years and many owners is a whole nuther layer of challenge.
As to getting your coach back on the road. It's a good idea to replace the fluids including brake fluid and the rubber parts. Tires, Belts, hoses etc. these 454s are a real workhorse of an engine. Good to also check the carb and Exhast system for leaks.
I'm not sure if the Argosies are built on the Chevy P 30 truck chassis as the classics are, but parts are pretty easy to find and not crazy in cost.
I like that you are planning to use your coach as is, we have many deep restorations under way in our crew, so may get to see you on the road one of these days. Have fun!