Forever.

In a cool, dark, place, it shouldn’t spoil for a long time. Liqueurs are more volatile.

Depends how you look at life and what you started off with. Younger cheaper whiskies can change character quite dramtically even over a short (relatively speaking) period of time but any whisky will begin to change once the bottle is opened. Some times the taste gets better some times it gets worse. As the bottle empties and there is more air left in the bottle the process can speed up. If you open and close the bottle alot this will also speed up the process.

Not forever but a long time. It’s a strong alcohol so germs and bacteria can’t live in it and it really won’t go stale like beer.

Pretty much till it’s gone. I’m more of a Jack Daniels drinker, though, and that never lasts long enough to worry about. Mm mm.

At my house about one night.