There isn’t a Stack or Plugin that does exactly what you want, at least as far as I’m aware. As you say there are a lot of ‘variables’ which makes it difficult to provide a package solution.
Availability calendars that you could look at incorporating include:
But I’ve found the small Hotel and B&B trade are using a number of channels (Booking.com, HomeAway, AirBNB etc) as well as their own website. To centralise a diary, take bookings online and update all the channels there are a numbers of services you can incorporate into your site. Take a look at these to get you started:
There are lots more, all of them require a £ subscription, and (in my opinion) none of them are perfect.
Good luck, and if you find (or build) a great solution at a reasonable price, please let me know.