I don't know how far you are planning to get into it but I'll give you my thoughts. You've already gotten advice all over the map so I don't know how you'll decide which advice to take. Maybe throw a dart. IMHO, any of the choices will get you 95%. Heavy lamp cord will get you 95%. All the tweeks and upgrades we do are looking for the last 5%, maybe the last 1%.
I've had very good luck lately with braided cables for both interconnects and speaker cables. I even bought one braided power cable. I braid my own interconnects. For speaker cables you can buy pre-braded wire usually either 16 or 24 conductors. Cheapest on ebay and looking at the pattern and colors it obviously all comes off the same production line. Your runs are long so that needs a heavier cable but unless you are running a lot of wpc, the 16 should be heavy enough. It is 10ga equivalent.
Plated OFC copper is always a good choice if you weave your own. There is lots of high quality wire that is surplus milspec out there cheap.
Just to be clear, this is advice for a newbie making his first set. I think these wires will do you very well. If you have a $100K system looking for the end-all cable, then wire choice would move up higher on the priority list.
Don't know what connectors you are thinking of using but look at low mass. This is something I'm doing. It isn't expensive but requires some thinking. You'll use low mass banana plugs on each end and eventually replace your binding posts, at least on the speaker end, with low mass binding posts. KLEI makes them. The theory is that a large mass of metal such as the binding post and to some extent the high mass banana plug disrupts the flow of electrons through the wire. the mechanical equivalent would be a pipe full of water with nice laminar flow headed to a far away location. The pipe enters a large lake and exits the other side. Sure the same amount of water exits but the laminar flow is lost and water is jumbled. This isn't even close to a perfect analogy since water doesn't carry information on it's wavefront but it's a way to think about it. Anyway, since you're buying connectors now it is a time to think about it. I'm doing it because it is one of the tweeks that a DIY friend who has highly modded the best system I've ever heard uses them.
Jerry
