Yes, everything Sehnsucht wrote.
Regions that use salt are often avoided due to rust. Engines produced 2004 or earlier (up to 2007, in some cases) will have less clean emissions devices, thereby saving maintenance.
Reading the historical record of wisdom, found in the search engine above, is only useful if you're persistent. The thread below is a good place to start.
Go to as many auctions as you can. Not to buy, go to preview and spend hours examining them. Crawl around underneath, open panels, smell liquids and compare bus differences. After some physical interaction, you'll be able to 'see' alot from the pics.
There are many different places to find and purchace a bus. Some are not advertised online. Take pics of prospects, post them here. Always best to physically examine 'the one' before you relenquish your cash. Good luck.