We got a great deal on a used Harman pellet stove a few years ago and tried it for one winter as an alternative to our coal stove. It did everything it was supposed to, was easy to operate and a lot cleaner than coal (still a little dusty but not bad), but it just didn't put out enough heat to keep the house much above 55 degrees. We also spent at least twice as much on fuel as we ever did with coal. The next season the coal stove went back in place, we went back to a toasty-warm house, and we sold the pellet stove for nearly three times what we paid for it
. A larger stove may have done a better job in terms of heat, but it still would have been at least double the cost of coal for fuel for the season.
1- You get convective heat (warming the air) and radiant heat (warming the walls, floor, ceiling), so it will heat beyond the room it's in, but make sure you get one properly sized for your house. Any legit stove dealer can help you do a couple quick calculations to determine the necessary capacity.
2- A little dusty, yes, but compared to coal it seemed super clean
. You'll have to dump ashes out periodically (depends on the stove, but probably once a day).
3- You can buy them in bulk if you have a hopper to store them in, or you can buy them in bags (they're sealed and can be stored outside, but if there is any moisture in the pellets they may freeze into a 50 pound brick).
4- Get something with a hopper on the back and an automated feed so you don't have to spoon-feed it every few hours.
5- Yes, because it didn't keep the house warm enough (was probably too small) and the fuel was significantly more expensive than coal (and a bigger stove would just make that worse). Coal is a lot of work, and dirty, but it's warm and cheap.