Hi Phil. Welcome to the forum. Here's some feedback:
1.Don't bother with the T parts - it's just marketing. In actual use, T and non-T parts will use about the same power. There's only $25 difference between the G620 and G860. If $25, doesn't bother you, then get the G860 and have some headroom. Either should work for your apps. In general, they are the same chip - certain features and multipliers are enabled as you go up in speed - so they all have the same reliabilty. The fan/CPU cooler is dependant on the case (ie: will it fit?). Got a case?
2. $175 might be limiting in the wrong area..H77 works as you don't need the hardware features of the Z77 and it saves you some $'s. Some choices to be made, though. ATX or a smaller mobo - depends on the case selection.
I wouldn't bother with a sound card. Try the integrated sound and see how well that works. You can always add an Asus Xonar card later. Don't think you need 8GB, but if you do, I like this.
3. I'd go with an SSD for the OS/Apps and a WD Scorpio Blue 500GB
for data storage. Intel is nice, as is Crucial M4 or Samsung 830. ~128GB should work.
4. As I mentioned privately, your power consumption will be low ( ~80W) and Pico-PSU seems to be a good fit. I'll leave it to the Pico PSU experts to chime in on details.
The audio thing: Don't get distracted by the 5.1 and 7.1 stuff. All integrated and sound cards can output stereo. As your speakers are powered, you won't need the Scythe amp.