sneamia,
You DO need to learn the Secret Handshake, but not the youngster handshake. You need to learn the Oldtimer Secret Handshake, the one that predates Apple I's, Commodore Pets, and TRS-80 Model I's; the one that dates back to when you gathered bags of parts, took soldering iron in hand, and actually BUILT something.
OK, seriously ...
I agree with tmlck. You probably do not need a 24 - 20 pin adapter. On all the newer PSU's that I have seen, the main connector is a 20 pin plug with the extra four pins as a small plug that you can clip onto it if you need 24 pins or remove if you need 20 pins.
The only thing that I will say about parts selection concerns the motherboard. I suggest that you find an inexpensive ATX board. It will be easier to work with and should give you more expansion options if you later choose to expand.
Building: I was going to suggest installing CPU, HSF, and memory before you put the board in the case, but I think with AMD CPU's you don't have any choice. For that matter, I recommend breadboarding the whole system. That way, you can test the parts before you install them in the case.
Also, take a look at:
http://www.tomswiki.com/page/Troubleshooting+a+New+Build
before you start. That may help you avoid problems that others have run into.
Good luck. Take care. Eat your vegetables, take your vitamins, read the motherboard manual before you start, and let us know how it goes.