>>3727
Fair warning. A complete answer to your first question is very long. PDF is relevant but really only a starting point. The big reason it's mostly hobbyists communicating with CW is that it's more involved but you see some interest in these kinds of discussions because of capabilities. Listening, on the other hand, requires very little and is not a bad place to start with CW.
Cheapest and most likely to find people to talk to would probably be a pre-built half-wave 40 meter (half waves so figure just a little longer than 20 meters) dipole antenna, however much RG58 you need to go from that antenna to your transceiver (higher is better), a one or two switch key for input, and a hobbyist QRP rig. There are more compact antennas but those are available, have good performance, and are not expensive. Hams are mostly old gear whores so pre-built stuff is typically very expensive. You'll see things like 300$+ transceivers and 100$+ iambic keys being the norm for low power operations, the latter of which is just two switches in a fancy box. There are a lot of low power hobbyist rigs for cheaper and most will assemble them for you if you're not in to electronics.
Hobbyists around the world do listen and communicate on the bands useful for long range CW. Amateur radio organizations are centered around emergency communication so it's almost certain someone would be listening in SHTF. How useful that is to you probably depends on what the situation is.