You say a Gaming/Editing machine. As in Video Editing?
Your going to want to put more of the budget towards graphics for a gaming rig, and far more power towards CPU and secondly RAm for a video editing machine.
You can't really have both in that budget range sadly, so figure out which is most important to you.
If the editing will be a occasional thing, just lean towards gaming. If editing is the most important, youll want to put more towards the CPU such as a Intel i5.
Also, I agree about the PSU. Get a good PSU, as its the heart of everything.
And while I myself am a firm supporter of dedicated audio card, that can wait untill later. A Good Power Supply is more important now.
As a FYI, keep in mind that while a dedicated audio card can make a significant difference in the audio, it will NOT make much difference at all over onboard unless you have some higher quality speakers/headphones to drive with it. Something to keep in mind.
I know I sound like a broken record to the regular members around here but:
For the power supply do yourself a favor and look into Corsair, Antec, Seasonic.
Yes, the 500-550W may cost the same or more than a cheaper 750W, but they may actually be far more powerful. Wattage does not mean everything.
A good 550 will be plenty, up to a 650.
One other suggestion, look into Gskill Memory. Fairly cheap vs other brands, but very good quality. Highly recommended.