Yes, XBMC is more flexible , that also means it requires more tweaking to get it just right
Good choice on the CPU - The "T" models really shine in silent builds - stick with stock/box cooler - it's fine
Don't over-think the PSU - 300W should be more than enough
I assume you are planning to use Ivy Bridge onchip video - I think it's a bold plan, but it just might work.
Do keep in mind intel video driver haven't been known for nor their features nor the polish - what I am trying to say that HD audio codecs HDMI pass-thru may or may not work