Let’s call it ‘quick’ not ‘worst’ scenario. To realize a quick scenario:
1) create separate roles;
2) include to them just capabilities which are required to access required part of WordPress;
3) if some required capability givea access to more than 1 menu items, including some menu items which you wish to hide/block from such role, use ‘Admin menu access’ add-on of the User Role Editor Pro in order to block those menu items.
To give you more detailed answer I need to look at the “Woocommerce Appointments” plugin, check and test it with different scenarios. I need to look, what it offers itself in the part of different access for the different users. You may send a copy of this plugin to support [at-sign] role-editor.com. I guarantee that it will be used only in the development (not public) environment and for the testing purpose only.
Double think before to give somebody the ability to install new plugins. Untrusted person may install malicious code and get full access to the site via it.