If I wake up and decide to brew an impromptu batch, can I begin a starter at the same time and just pitch the next day?
Seems comparable to no-chill brewing as far as contamination concerns, though I would still plan to use my IC and rack to my carboy on brew day.
If I do this, what about aerating the wort? Do it on brew day, right before pitching yeast, or both? Anything I'm not thinking of? Thanks!
You should be fine doing this. Don't aerate until the next day. For an added clarity benefit, if you are chilling all the way to pitching temp on brewday (or at least belo 130-140), you can 'decant' the wort the next day into a different sanitized fermenter and leave the trub behind. This can also help to aerate. FURTHER, this will also basically allow you to harvest almost pure yeast from the bottom of this batch, that won't need a lot (if any rinsing).
I think it's just a matter of preference. If you rack to a carboy and store it cool, then the few microbes in the airspace will not cause too much trouble before morning.
However, I personally feel that once the wort is ready to pitch it's preferable to pitch the starter then - even if it's only been stirring for 8 hours - since it ensures you have the lowest chance of contaminants taking hold. The yeast will have already gone through at least one budding and are going "full throttle" so your main brew will also take off quickly. And assuming your starter was from a vial of healthy yeast and that this is a moderate (<1.060) strength beer, the amount of underpitching (if any) is not worth worrying about. But for other cases, such as harvested yeast, and high gravity beers, you should definitely let the starter go to ensure you hit appropriate pitching rates, or better still plan ahead! :)
