PSU: get a higher quality, lower capacity PSU. For a single video card, a 550 watt Corsair would do nicely. I'd get a 650 watt Corsair or Antec. (I recommend what I use.) But I prefer to operate my PSU's at 50% - 60% of capacity.
HD: Get a WD 640 Black (two 320 GB platters) or a WD 1 TB Black (three 320 GB + platters) instead of a 750 GB drive (three 250 GB platters). Faster.
Case: You will need a case speaker. Antec 900's do not come with one.
And while you are waiting for your parts to arrive, take a look at this thread:
Our standard checklist and troubleshooting thread:http://www.tomshardware.com/forum/261145-31-read-posting-boot-problems
It may help you to avoid some common mistakes.