Ability to Limit Available Dates in Custom Date Field

We have a custom field our customers use to schedule their preferred service date. It would be nice to be able to limit what dates are available to the customer. Not only would we find a list of blackout dates useful, but it would be amazing to limit the number of tickets that can have the same date selected for a given field. Currently, we have to monitor this manually and contact our customers after they have submitted their ticket to ask if they are willing to reschedule.