Odoo 12.0, complex export/import of custom data

There is a project management system based on Odoo 12.0 and a self-written add-on to it with many interrelated own models.
You want to get some data out of this system and put it in another such system.
That is, in my understanding, it should work like this: in any list of records on the backend, I select a certain number of records, and on command they are exported to XLS (or somewhere else, but in XLS it seems to be simpler and more familiar) in such a way that the export contains:
* values of all fields that are not calculated, but just fields
* identifiers for all fields m2o and m2m,
* and the same lists for all related records of other models linked via m2o and m2m, so that when you import all this, all records and all connections between records are also restored. That is, so that this part of the structure can be transferred to another similar system - without creating this system from scratch entirely, but namely adding to existing records - transferred. Optionally, you still want to immediately transfer files in the same way if they are stored in the system as files (and not as binary fields in the database)
Perhaps such an add-on already exists, only I do not know about it?
But if it doesnt exist, then it needs to be written.
PS: Please offer a price right away.