Using the plugin APPOINTMENT + I have observed that it has an important limitation in their use.
The capacity limit is associated with the service when it should be associated with the limit of the capacity of the facilities.
For example, a room can be used to provide various services, but I can not provide more than one service at a time per room. In addition, several service providers can offer the same service. In this way the system could admit appointments about services but without sufficient rooms, because I still have enough service providers.
Therefore, for the plugin to work reliably on many businesses, it would require a new entity to identify the facilities available, which remained associated with certain services, to set the limit of the capacity to provide services.
I just become a member of WPMU DEV and I do not know if it's possible to change that.
I look forward to your answer.