Got some questions! Broad range..

[4jacks]

If your going to get dual exhaust, Please get a new back bumber cover that has holes for it... AKA Black widow.. otherwise it's kinda corny.. IMO
I'm sure thousands of people have gone dual on a Civic before, you will need a shop that bends pipe. such as Midas or minieke or one of the million small muffler shops to do it. Buy two Free Flow Mufflers off of Ebay or where ever you wanna get them. take them to the shop and just pretend that you know what your talking about. tell them you want 2.25" or 2.5" pipe, split at the cat to dual exhaust and tell them where you want the mufflers to sit.
when I was A Prober, We could not really do that due to the fact that the bump from the spare tire was in the way... I haven't really looked under my civic too much, but you may wanna do such a thing.

Also plan to spend at least $300 on dual pipe work .

But the best thing you can do is go have midas put your car on the jacks and take a look at it. They'll do it for free... just act sticker shocked, and tell em your freind had it done way cheaper on his 240 or sumptin and then tell em your going check around for prices and you may be back.

i went to 6 shops before i had my muffler put on =) original quote $260 ... final price $170