1) you are giving in to marketing hype. Paired spokes are not necessarily lighter, it is just a single lacing pattern developed by Rolf and then stolen by trek/bontrager. There are many lacing patterns, and MANY better wheels than those made by rolf/bontrager.
2) Aluminum with a carbon fork and maybe rear stays would probably be in your price range. Check out some of the current offerings from Performancebike.com, I think they have some in the 1000-1200 range with the carbon bits
3) As components get better, they get lighter, crisper, and usually more durable. Try to stay away from Sora, the shifters seem to have been designed by a blind mentally deficient monkey. Tiagra (right above Sora) and 105 are near your price range, so look for a bike that comes with these levels.
4) Find out what size you need at your local bike shop, and see if you can get a deal there first. Always better to support the local guys. If you can't get a deal, you will at least know what size you are so you can get the right size bike at bikedirect or some similar online company. Be warned though, if you bring your bikesdirect bike into the shop to get fit, they aren't going be all that happy with you.
5) Building your own bike will almost never be cheaper, unless you get everything at super deals (on ebay and the suchlike). Bike companies get components much cheaper than you can, and they usually pass on that savings in the cost of the whole bike.