Real quick -

CMH overnights vary by base from month to month and schedule changes. No good answer there. Whatever I told you would only be a snapshot. If you live there, MDW or BWI would probably be a good bet.

Last time I checked, commuter policy is to try at least two flights prior to your report. If you can't make it, skeds will pull flights with no pay until they can get you back to to your trip.