Hey Lynn,
I definitely was fast asleep being 3 am or something here.
I have an iMac running OS X (10.7.5) and I use iMovie '11 (version 9.0.8). It produces .m4v files. All I do to make it suitable for the busking and review uploaders is to drag a copy of the file to my desktop and then simply rename it a .mp4 file. Tony taught me this trick.
That's it. There's no conversion involved unless it happens in the iMac itself. I'm simply changing the name and that's enough to fool the uploader into accepting it. Occasionally some of the sound and/or video quality is lost, but most of the time it's fine.
If yours are .mov files then I presume you are exporting out of iMovie using QuickTime (an export option from the iMovie program) or maybe you're using QuickTime itself. I'm not familiar with using quickTime to record, so you'll need to seek other advice there. Have you tried the Apple community help pages.
https://discussions.apple.com/index.jspa just like this forum, the Apple community will help you with what ever you need if they have the info.
I'm actually thinking of changing to Final Cut next year because iMovie isn't handling all of the separate videos and tracks I try to squeeze in. My mac is getting a little too old for it too.
Mics, I've used various things, the mic in the Mac, a Blue SnowBall USB mic (plugs straight into your mac) a Apogee MiC USB and recording on my iPhone via HD Voice Recorder (an app) and cutting that in later via iMove or GarageBand. If you've got a pickup on your guitar, you can record into GarageBand (straight to the iPad using Apogee Jam - then I send the file to my Mac and mix it in GarageBand) or via a intermediate device (that I haven't got or worked out yet - but there are members who so use that approach).
Gosh it sounds like a major production:) if only I had the skills like you and Vanessa to make it all worthwhile.
So if you use iMove, then choose 'Export Movie...' From the share menu and then just change the name from .mv4 to .mp4 I assume that you export straight to YouTube at the moment. Once you have the file with the right extension, just open TG and the appropriate uploader and then select the right file from your iFinder menu or drag it from your desktop.
It's easy once you know what the uploader needs.
Enjoy.
Shel