Welcome aboard the crazy bus! A few thoughts to help in your journey... Consider that a front-engine bus is hotter and noisier for the driver than a conventional dog-nose or a rear-engine pusher. However, rear-engine pushers have their own special set of nuances, some having cooling issues due to the radiator having insufficient airflow under certain conditions.
I'm not saying NOT to buy a front-engine flatnose, just know up-front that it would be wise to insulate and/or DynaMat the doghouse.
Also, know that these are school buses, not over-the-road coaches. Most top out around 55-60 flat-out, and don't expect to get great fuel economy. These are big, heavy vehicles with commercial diesel engines. You don't say specifically what your experience with diesel is, but most of these engines probably weigh more than any vehicle you've driven before. Not meant as an insult, mind you. I don't assume what people DO know any more than I assume what they DON"T know. It's a different world -- ask lots of questions, there are more than enough friendly folks here who are all too happy to guide you.
Also know that it is wise to seek advice here before jumping on a purchase -- Some people are scammers, and there are even a few that lurk here from time to time, trying to peddle junk, though we do our best to run them out of town on a rail. Just because someone is a bus 'dealer', doesn't mean their wares are worthy. A former member here bought one from a self-professed 'honorable' and 'reputable' dealer, only to have the transmission die within a month (not covered by the seller's 'tail light warranty'). A 'tail light warranty', by the way, expires when the tail lights have disappeared from the seller's view.
And don't take government auction listings at their word -- I bought an ex-police car through online government auction that was listed as being serviceable and only being retired due to age. An $1180 bid got me an engine that was shot and cost $1800 to replace. It drove home, so I guess that was their definition of being 'serviceable'. Anyway, look before you leap... Inspect in-person, and it helps to have a knowledgeable bus or heavy truck mechanic available, especially if they can tag along to look it over for you in person. Remember, once you buy it, it's yours -- including any problems it may have. More zeroes when a bus or heavy truck has problems.
Also, if you get one that has air brakes... Please do your diligence in education on how these systems work... Air brakes are not complicated as long as everything works the way it is supposed to, but there are certain things you need to know in order to keep your bus, yourself, and others around you, safe. I happen to be a CDL holder with 4 years experience over-the-road, and there are at least three other members I know of here that are happy to help with experienced advice on this particular aspect.