Need some newbie advice on speaker wire

Sup yall. This is my first home theater setup and was wanting a bit of advice on my 5.1 setup. I just want to make sure I get things right the first time around. Because of the room I'm putting it in I have to snake my rear speaker wires and my sub cable under the carpet. My rear speakers will run 15 feet under plus about 5 feet for slack and to run up the shelf or stand(haven't decided). My sub will run about 20 feet under carpet. My front towers will just be about 4 feet away from the receiver. And my center will just be about 3 feet above my receiver.
A couple questions I had were:
What gauge of speaker wire should I run to my fronts/center?
What gauge of wire should I run for under the carpet for my rears?
What is a good place to get some flat speaker wire?

As well any other advice/feedback would be greatly appreciated.

Thanks ahead of time yall.

My set up is:
(All speakers from av123)
Fronts: x-statik Open Baffle Loudspeakers
Center: x-voce Open Baffle Center Loudspeaker
Rears: ELT525M Mini Monitors
Sub: MFW-15 Subwoofer

A/V Receiver: Onkyo TX-NR708 (as soon as it goes on sale in July)
Possible Amplifier: Emotiva XPA-5

Right, I want to try to get flat wire so I don't have a bulged if any in the carpet. And if possible a flat cable for the sub.

I see alot of them.. But they are just saying it can be used for under carpet use. Should I worry about it not being cl2 rated?

I really don't want to but I would have to replace pieces of sheet rock and paint if I run them thru the ceiling.... Not to mention I have no clue if there are cross beams going across since its in a downstairs room. And I would run it thru the base board but there are doors in the way.

Yea I ordered them from the bstock/open box section of av123.. They look brand spankin new tho..

Kool thx... I'll have to check them out. I could only find 16gauge flat on-line form parts express.

thx all for the advice yall... and thx theformerpro i bought that wire from radio shack thats exactly what i needed for my rears.. i think for my fronts tho im going to go with the dayton cables that have the banana plugs already on them so i can get a cleaner look.