No the extra power is not drawn, and using a higher wattage psu will on lower consuming parts would be more efficient (most review sites do this). However, the higher the wattage, the better the quality must be since it's going to be even bigger and hotter than the averege ones. Many PSUs just die after 2 years of normal use, so watch out for the branded but budget PSUs, especially the lighter ones, a heavy power supply is usually a good pwr supply.
I'd reccomend you get the latest generation of graphics cards whenever you're investing so much money, since you want longevivity of the system. Get a simmilarly priced 700 series card (770, 780 if you cut out the OS and maybe a cheaper motherboard which you really don't need, use a student key from a semi-illicit forum or just bypass activation, you won't lose anything, other than your integrity on this forum).
If you notice too much power wasted during idle, you'd want to set some time to undervolt and underclock the processor and graphics card (they do this automatically but you can still change some settings, would reccomend a gpu overclocking tool like rivatuner or msi afterburner).
For the usage you stated you won't need any more RAM than 8 GB at this time, especially for games who (atm) rarely use over 4. You must use your bought kit so you can take advantage of dual channel capability of system memory (if you add an odd module you won't be able to use it, if you add another kit like the one you bought - same model, same speeds - then it will still be dual channel albeit a bit slower, depending on the motherboard chipset, it's a hardware engineering problem I didn't understand :P, but I'm sure there are more documented folk around.
Keep my suggestion in mind, you'll be really thankful in the long run if you skimped on some of the parts and buy the latest and greatest video card you can afford (there's cheaper ram, you don't really need an SSD, you can get an external usb 3.0 drive later, there's newer better video cards).
Then you will be somewhat futureproof, because the PC industry is supposedly quickly evolving (although it kind of stood still for about 3 years)