IPhone :: Temporarily Emptying 4s Storage For Video Recording?

I'm getting married soon, and rather than hire a videographer to produce something we probably won't like anyway, we thought we'd go down the riskier route of asking friends and family to use their iPhones to record video on the day, and then editing all the results together ourselves.

The major stumbling block we're facing now is that most people's iPhones don't have enough free storage available to be used as video cameras for a day-long event. So I was wondering if there was any safe way to back up each iPhone (we're talking about half a dozen or so), temporarily reset it to clean out the storage, and then restore it later on after extracting the video. The questions I need answered are:

1) Can one Mac, running one instance of iTunes, be used to back up multiple iPhones, some of which are not even synced with that specific Mac?

2) Can I get large amounts of video off those iPhones without syncing and potentially over-writing previous back-ups? Is there a method of extracting video that doesn't involve iTunes (just as you can use Preview in OS X to get photos off the camera roll without opening iTunes, for example)?

3) Once the video has been taken off the phones, is it safe to assume that iTunes will happily restore each phone from its respective back-up?

Info:
iPhone 4S, iOS 5.1.1