1) That's a lot of money for those cables. Why not Blue Jeans 10 gauge? Great quality, low price. Probably won't notice a difference in any case compared to what you have now. I'd spend that $1000 on a new sub!
3) Your sub should work in stereo, only way it shouldn't is what jliedeka mentioned. Go to "channel level" and play a test tone, does anything come out of the sub?
4) Speakers can handle more clean power than they are rated for, you'd be fine to do this. But as jliedeka mentioned, you probably won't notice a difference.
5) You'll be fine without regulating it. Just don't crank it to 11.