Definitely get a good wiring kit. The more strands, the better. And make sure everything is properly fused and grounded. Also, use good RCA's. A cleaner signal produces a cleaner sound.
1. ) It will reflect sound quality, but not lifespan.
2. ) You should definitely go for your budget range-- as much as you can spend. The bigger the better (Now, realize: Don't get too big of wire that won't fit into your amp) Also, go for a higher strand count over a lower one. Not all 0Gauge is the same size //content.invisioncic.com/y282845/emoticons/fyi.gif.9f1f679348da7204ce960cfc74bca8e0.gif. There's a lot of pictures on here with two zero-gauges next to each other and one is significantly bigger than the other. You just have to check your source. A really popular place is http://www.knukonceptz.com Their flex series is supposed to be really good. That's where I'm getting my 0/1 gauge for my big 3 //content.invisioncic.com/y282845/emoticons/fyi.gif.9f1f679348da7204ce960cfc74bca8e0.gif.
And as integra88 said, fuse the wires. Now, I know some people are iffy about fusing the wires from the amp to sub... and I'm honestly not sure if you should. But the + and - to the amp you should definitely fuse. You can find inline fuse holders, circuit breakers, or distro blocks with fuses in them. Also, don't skimp on the fuse. Get the proper ampere fuse. It's useless if you get it too big or too small.
You can go either way, but if you get an unfused distro block, make sure to buy some inline fuses. Streetwires had a badass fused combo block for the power and grounds which has fuses but they don't make them anymore. Luckily a local shop had one so I got one myself and I love it.