@Jeana30 I was on VRBO instant book for many years before also advertising on AirBnB. I do use instant booking for both sites, but I am at my computer most of the day and can check for issues immediately upon notification of a booking. I have occasionally turned off instant booking on VRBO and have found that I still book well through them -- most of my VRBO guests want to communicate prior to booking anyway. Turning off instant booking allows you the time to review a booking request and say yes or no.
1. I do not include tentative bookings in my calendar sync. Paid reservations only.
2. I monitor the calendar sync daily and have never had a double booking. Knock wood.
3. There is a checkbox on the VRBO site under Rooms and Spaces where you can accept long term guests. I have this checkbox unchecked, and I do not offer discounts for a rental over 2 weeks duration. This has deterred most long term guests as my month price is now too high compared to my competition.
Using more than one platform will ensure that you have more consistent bookings, but like any business, your time and attention to your rental is important. This is not a set it and forget it business.