To achieve this in Odoo 16, you can use the following steps:

1. Create Employee Shifts:

In the "Planning" app, you can create employee shifts for each consultant. These shifts should include the working hours for the consultant. You can also create shifts for consultants who are not currently assigned to any orders.

1. Create Appointments:

In the "Calendar" app, you can create appointments for each consultant based on their availability. You can link the consultant's shift to their calendar availability using the "Shifts" tab in the appointment form. This will ensure that only the available time slots are visible to customers.

1. Publish Employee Availability:

You can allow customers to check employee availability by publishing the employee's calendar on the website. This can be done by enabling the "Website Calendar" feature in the employee form. Once this feature is enabled, the employee's calendar will be displayed on their public profile page.

1. Allow Self-Booking:

To allow customers to self-book appointments, you can create a custom form on your website that allows them to select the consultant, date, and time slot. You can then use Odoo's built-in web form functionality to capture the customer's booking information and create an appointment in the "Calendar" app.

1. Send Notifications:

To keep both the consultant and the customer informed about the appointment, you can configure Odoo to send email notifications to both parties when an appointment is booked or updated. This can be done by configuring the "Notification Templates" in the "Settings" menu.

By following these steps, you can combine the functionality of the "Calendar" and "Planning" apps in Odoo 16 to plan employee assignments and allow customers to self-book appointments based on employee availability.