Look at the calendar during the busy season (January - April) and check how many days are booked off.

Shall we try to get a happy hour or something on the calendar?

Also, I'm toying with the idea of only doing VRBO and not Airbnb because I've read a lot of anti-AB feedback in STR owner FB groups lately, and that the quality of guest seems to vary (though VRBO has its bad apples too), and it would keep me from trying to manager too much/synchronize calendars, etc.

Once you can do this your calendar should begin booking easier and easier and then you can begin to raise rates to achieve your ideal occupancy.

It would be great if furnished finder had the calendar rate option.

But in general, it gives a good overview of your competitors' data for the last 12 months, which you can't get by the "enemy method" of looking at competitors' current calendars, which only shows the future. 

Peak at their calendars and reviews to get a better idea of what guests are loving about that location.

Is there a good platform or calendar that people are using to tie all three of these booking resources together?

Not sure how the calendars (bookings) would integrate. 

If you go to their website they have a calendar with all their meetings and information.