The prices are all on the web site
Power Hungry Performance - Feed your hunger for POWER!, To switch on the fly you will need a phoenix chip, then gauges aren't a bad idea, so you could get the edge insight (PHP sells those).
for a high idle tune, the Phoenix is a good choice as well, that way you can switch between the high idle and a normal tune without issues.
The CTS has the touch screen, it is larger, and it has a backup camera option available, other than that it is the same.
Yes you can get a used CS or CTS and have custom tunes loaded, you would need to provide the serial number (or something like that) to PHP so they can get you your tunes when they are ready, all you would do is update the CS or CTS through the program provided by edge.
What other questions can i help with? BTW I am planning on doing the phoenix/insight combo once I get the money.