do soundbars hook up directly to the tv?
Yes if you want. Many sounbars offer multiple inputs so you can hook up to TV or other devices, or both.
- every time I turn on the tv, will the sound automatically come out of the soundbar?
Yes on some bars, no on most.
- do I need a receiver?
Not for the soundbars in your price range.
- can I expect 5.1 sound, and if so is that only in higher end soundbars?
Soundbars can give surround effects, but if you want 5.1, buy 5.1
- I assume I should really get a soundbar with a subwoofer, but is that a good assumption?
- do 'wireless' subwoofers work well? how are they powered with no wire?
Yes they work well. They must be plugged in for electrical power, but communicate with the bar/amp via wireless signal. Some owners of wireless subs experience problems if they have wireless networks.
- anything specific I should look for in a soundbar, as far as connections or power requirements?
You will want optical connection at least. If I'm not mistaken, your TV does not support RCA analog output. This is the case at least with this year's Samsung C630 and C650 models.
- can I get certain cables ahead of time, or will it depend on the soundbar?
Yes, you can buy cables ahead of time, but you may not need to, depending on the soundbar and how you choose to hook everything up.