1. Yes, the ends are finished and the installers will correctly install the runner (s) so that any place where you have an "ending" will end up with a finished edge. However, the ends are NOT finished at the very bottom and top of the stairs; so - what the installers do is to either fold the carpet over itself or just make it flush with your floor and the top of the landing. (The latter is what they did with my installation and it looks very nice. )
(The installers also ASKED me what I wanted at the ends and SHOWED me the two possible options. I really appreciated this because I didn't realize there were two options.)
Logically, you cannot have more than two finished edges on a piece of carpet roll; but what was nice is that the man who initially came to take measurements KNEW this and correctly ordered TWO pieces so that the edges would be finished on my landing where the direction of the carpet changes. I had not thought of this myself but was so pleased that the man who took the measurements DID know that this would be important and took this into account and ordered TWO pieces of carpeting.
The SIDES of the carpet runner are also finished: NO possibility for fraying on the side edges, either.
The end result is a very polished look with absolutely NO AREAS for possible fraying in the future.
2. Yes - You can order finished runners to the inch , if you like; but the STAIR carpeting comes in rolls of pre- determined lengths. So, about 10 feet was left over from my job and I intend to use this 10 foot piece for an area runner. (They will give you whatever is left over - you have paid for it.) You can take it to HD and they will have the same installer sew a finished edge around the rug you desire for a reasonable price.
I hope I have answered your questions adequately.