Cmode questions

[NetNomad]

I've been playing a bit of cmode lately, and I have a few general questions:

Good map/bad map: I hear people talking about these... how do you know what's a "good map" and a "bad map?" And what's so good about a "good map?" I've read some guides here and on PSOW but I haven't found a clear explanation on this yet.

Clear times/TA times: I don't see the purposes of these... originally I thought TA times were the required times for S-Rank, but apparently this is not so; I added up the times in PSOW's clear time list and it came to just under 7 hours. So what are the TA times for?

Clearing and re-clearing: I've already seen that you can re-do a stage and save your original time. But what about c9? Do you only have one shot at c9? What if I need to play c9 just do learn the maps and puzzles... do I just purposely die at the end? Are there teams willing to do this? :S

Thanks alot.