I wouldn’t key in FCP. It’s not that great. Use After Effects if you have it, otherwise use the Primatte RT keyer in Motion. You will have less headaches and be happier with the results. Of course, that’s just my opinion.
Did you render after getting your colors corrected. That flicker is always there for me until I render the clips (a preview green line above the clips?).
I usually right click (control click) and choose copy. Then click on the spot where you what to paste and right click (control click) and choose paste.
I would double check your system preferences. Go into energy saver and make sure to uncheck the box that says “Put the hard drive(s) to sleep when possible.
Highlight image in the timeline and apply the filter, then double click the image. If I was trying to key out the white in an image, I would use the Luma Key. But that’s just me.
You should just be able to import a wav file, but if you do want to convert it to an aiff, just bring it into itunes to convert it (which I often do for mp3s).
Go to the top middle above your viewer and there are three buttons. Click on the one on the right and go down and click on RGB instead of Alpha. That should do it.