SWA on a TN-C-S or TN-S supply does not need any RCD. If installing the Zappi, it would be preferable to have a non-RCD circuit for it in SWA throughout.
The Zappi product includes all of the required RCD and DC leakage protection.
Harvi is an optional device to connect current monitoring wirelessly, rather than using a cable.
The hub is a separate item required to connect the Zappi, Harvi and other devices from that manufacturer to the internet, so you can use the smartphone app to control and monitor it and various other things.
New circuits and consumer units are notifiable work under the Building Regulations (Part P). That can either be done direct to building control or by an electrician registered with one of the schemes such as NICEIC or NAPIT.
New circuits should also have an installation certificate as required by BS7671 which is completed by the installing electrician. That will contain full details of the work done and all test results for the new circuits installed.
EV chargers are additionally notifiable to the DNO for load management purposes. Example:
https://www.ssen.co.uk/Connections/EVconnections/
The arrangement there is that the installer does a load assessment for the existing installation. If the total load including the new charger is less than 60A, the install can usually go ahead with just the notification.
If it's more than 60A, DNO confirmation must be obtained before installing, and in some cases additional works will be required by the DNO to upgrade/alter the network to accommodate the additional load. That may or may not be chargeable depending on who the DNO is and various other factors.
Regardless of total load, some locations won't be usable without further works, such as looped supplies or blocks of flats where the building has a single supply and multiple EV units are required.
All of the above should be done by the EV installer. That's why installing EV charge outlets is expensive.