Re: Buying a bus-thought
I think getting one that is in mechanically good shape doesn't necessarily mean it needs to be newer...but that helps. Obviously a close inspection will be the best thing for you.
Another thing to think about is not the year of the bus persay, but the year (or years as it may be) of the parts used. A bus in great shape with a low miles 9.0 International might not be a good choice simple because it has a 9.0 which was never extremely popular and has been out of production for a long time making the parts more expensive.
I think that if you were to stick to a DT360, DT466, 6BT, 6CT, 7.3 IDI, 7.3 DI, 3208, 3116, 3126, etc for an engine you will be best off.
Ditto for the transmission. I didn't see you post if you preferred a manual or automatic, but you would be safe with an AT545 or MT643. If you were to get into an AT540 you MIGHT have some problems. Ditto for a fossil of a 5 speed. No, they don't commonly break, but when they do...ouch.
Brakes are another thing to look at. Air brakes with good old fashioned manual slack adjusters don't get much cheaper, easier, reliable, or universal. Hydraulic brakes can also be pretty universal (though not QUITE as much), but you want to avoid some of the bastard children like the Lewis-Girling brakes Ford liked so much.
Beyond that it's all just a judgement call. Stuff happens. Just start with the best mechanicals you can afford and find. And don't forget the body either...pulling out a floor and walls to patch rust holes 2 years down the road doesn't sound like a good time to me.