1) It's a good idea. I use the analog (ones with the needle/dial readout) to get a general idea at a glance of what is going on, but rely on the digitals w/ probes for more accurate readings. People got away without them for many years but the make life much more simple.
2) I personally only use one per tub and it covers about 1/4 - 1/2 of the bottom depending on the tub. The important thing isn't how many you use but are you able to provide the right temps for your snake.
3) No it doesn't. It is "cage appeal". News paper, a hide and a water bowl are more than enough.
4) You shouldn't need a light to keep heat up if you have things set up properly. A UTH should be plenty to maintain the temperature. Guess I should ask if you're using a glass tank or a plastic tub? If a tank consider a tub.
5) One more reason to go with plastic tubs. Humidity is so easy to maintain in plastic tubs.