Hi Marc,
Bringing AVIs into M100 (or anything else on the Mac, really) can be tricky. Having said that, what version of M100 are you using? We did recently have a problem importing some movies that weren’t exactly 720×486, but that problem was with the horizontal scaling. That shouldn’t be the issue with the footage you’re describing. I would shy away from AVIs and try MOVs instead.
In regards to your original question, I would definitely request 720×486.
Where the codec is concerned the general rule is that if QuickTime can play it, M100 can import it. Some codecs, like the ones available in M100’s Media Settings (as well as a few others such as Animation) can be “quick imported”. Bringing them into the bin almost instantly.
The most important concern is that you are aware of the color space of the codecs to import vs. the color space of the media in your timeline. Media 100 can mix and match YUV and RGB color spaces in real-time just fine out to a deck or an external monitor. However, if you need to export the program, there can be only One (color space, that is). If you export a timeline with both color spaces in it, one of them will either look washed out or crushed.
The only way to be sure this won’t be an issue is to do a quick workflow test with a short, sample Program. It’s best to import files that already match the color space of your existing media, but you can also switch the color space in M100’s Import dialog if need be.