Best advice, shop for a bus at the local bus barn (school district bus parking area) through the Public Surplus or Federal auctions.
http://www.govliquidation.com/
https://www.govdeals.com/
http://www.publicsurplus.com/
Most of us here don't like buying buses from re-sellers. People say they feel at risk during the auctions. Consider who has more reason to pawn a bad bus off on you, a county agency or a bus re-seller that stands to make a profit? I'd prefer a bus that has been recently pulled from service, simply because I know it has had frequent use rather than buying a bus that has been sitting in someone's backyard for who knows how long.
Additionally, most of us here don't like Cat engines because of their propriatory parts that are considerably expensive compared to International and Cummins parts. There are also people that prefer Cat engines, so do what you're comfortable with.
You didn't mention if those brakes were air or wet brakes. Again it's a personal choice, but most of us prefer air because they're safer and more durable.
You'd do well to read information on anything you have questions about. It works best if you search subjects through google; i.e. "brakes, skoolie.net" or "insulation, skoolie.net."
Are you thinking of making the weekend camper type bus or are you thinking of doing a full build to live in?