Google-calendar – Creating a Google calendar event on specific days using IFTTT

You can't select which calendar in Quick Add. However if you add event by clicking on your calender grid, you can bring up a dialog which allows you to select your calendar. That's pretty quick to me too. E.g. I can say "@7am dentist appt", then select a calendar, then submit, this doesn't go through the full calendar configuration screen.

Yes, there is a Google Calendar API and they also have a command line utility called GoogleCL.