There are a large number of questions here.
I would make the following points to you
I've never built nor overclocked a computer before
Building a computer - today - is not that complicated.
Motherboard headers and their connections from the front usb ports and front audio and panel for the Power, reset etc are mainly block connectors and it is generally more DIFFICULT than EASY to connect them incorrectly.
This was NOT the case a few years ago when all were separate wires and you could MORE easily - connect a ground to a powered output - usually an error with drastic consequences.
HOWEVER there are still mistakes and errors EASILY made - such as
1. Forgetting to remove any protective film from pre-applied Thermal compound on the CPU cooler - not ALL have a protective film
2. Forgetting to connect the CPU fan header.
3. Failing to take proper anti-static precautions
4. Attempting to insert the CPU incorrectly - normally identified by an arrow or corner shape. It will NOT GO IN, but a pin is damaged in the attempt to do so.
5. Motherboard secured incorrectly - stand off etc.
and the list goes on.
THIS is not to worry YOU unduly, but this is an expensive build and you WOULD NOT be the first person to get it wrong - nor certainly the LAST.
MY ADVICE if you do NOT have experience of the inside of a computer case and have NEVER installed Graphics, ram HDD etc is DO NOT LEARN ON THIS BUILD.
Beg, borrow or buy the cheapest computer you can find, maybe one of your acquaintances has one that is beyond its service life but is still working OR perhaps you have one.
Take it completely to pieces, as far as you can. NO need to remove the CPU itself especially. Then rebuild it. If it works SUCCESS.
If it does NOT work - then it is probably the most useful exercise you have undertaken AS - IT COULD HAVE BEEN your new expensive BUILD
NO. I made no suggestion that the EVGA card would not work
I simply offered you the consideration of examining further your planned purchase.
If it was me NOT that I would require such system as I do not GAME or even require high quality graphics - I am a great believer in staying as close as posible to what the chip manufacturer intended. Nvidia states that the chip runs at 732.
EVGA have superclocked it to 797.
IN MY OPINION - overclocking is to be AVOIDED at all costs.
The reason manufacturers produce guides etc and setups that can be overclocked is in response to public demand.
My experience is that the benefits gained are VERY SMALL compared with the RISKS involved.
That is NOT in respect of that graphics card per se, but in respect of OC in general.
I've read there will be wasted power, but is that ever so bad? Just wondering.
I think I have already answered that. IF THE system demands 450 watts a 650 watt PSU will supply that and ONLY that
That is the case WHATEVER the wattage of the PSU.
What you have to bear in mind is if you MAY go for TWO cards to share the load on the graphics - then you may need to re-exmaine your PSU
HOWEVER as I said my colleague Digerati is the expert on those matters.