Youíre probably not going to get many answers on this post because it is something that is posted and discussed very often on this site.
Mileage: varies but expect 10ish
Buying online: if you can get a good deal and you know exactly what you are looking for, go for it. I would have bought online if I didnít find a good deal nearby.
My advice: do more research before you buy! Not a dig, but based on your questions you need to read up a little more. Know exactly what year/model/engine/trans is best for every year or model you are looking at, and know all the potential red flags of every model you are looking at.
P.S I bought my bus a little over a month ago so I just went through the research phase. Itís a pain in the ass but Iím so happy I waited, researched, and planned ahead of time. I settled with a 2003 international DT44 23.5 feet from Arizona. I paid $6900 out the door.