I prefer corn cob. It does not clean as fast as walnut, but it cleans shinier.

50 pounds for $37 at Grainger. That is a LOT of media.

How long to tumble is a factor of how dirty the cases are so that is nearly impossible to make a blanket statement on other than a pretty pointless one; "until it is clean". Expect it to take a couple of hours at least if you are like me and really enjoy loading cases that look like they are made of gold.

Dust. Yes. Eventually. 'course if you have 50 pounds of it . . . . you can change it when you start getting annoyed by it.

Most of us use some kind of tumbling media additive. Most commonly called "case polish". I get exceptionally cost effective service out of "NewFinish Once a Year Car Polish". It also really helps keep the dust down. Anyway . . . most modern liquid polish/wax that does not contain ammonia will probably do just fine. My point is that you can get a quart for about the same price as a pint of "cartridge case polish" and get it locally to boot.