From the dvd, the hda and ac97 are for the jacks on the front of the drive, so if you want to plug headphone in plug the hda in, I assume your motherboard has hi def audio.
And the switches, just adjust the fan speed, I'm not sure if you'd want them on low/medium. Suppose you could run something like hwmonitor and have the fan switch to low, see what the temps are, then change the fan switch to medium/high, see if there's any real difference.
What power button on the motherboard? doesn't seem to be one, and no lights on the motherboard.
when you've built a few without a hitch you will say its easy ,but the first time is a bit daunting' best advice is take your time and ask if you are unsure.
We put the fan on the cpu with thermal paste on but we took it off again and put it back on without renewing the paste, would that make a difference? and yep with the ram/memory and psu facing upwards.