Cheritto's Importer

No, the plugin will only add new data.

Yes, as long as they belong to the same export job (usually, multiple files come from an export done via ‘wp cli’).
If they do not come from the same export job, you will have to go through the import procedure for each xml file.

You can choose to import all as is or to check if posts or pages with same title, date and type already exist, in which case they won’t be imported.
In any case, authors, categories and tags will never be duplicated; only added if not existing.

The importer will create new users with role ‘author’ if no user exists with the same email or nicename.
A random password will be generated, authors have to reset this password to login.

During the check phase, all files are read and parsed, and data converted in database tables, while during the import phase, data is transferred only between database tables.
The difference in speed is more evident with large file(s).

During the download phase, the importer must make a request and save the image.
Depending on the ability of the called server to handle requests, it may take a while to complete for a large number of images.

The importer page uses and independent check to verify that the job is running and it does so at every page load, so if you see ‘Check is running’ it means that all is going fine.
If this check fails for more than a minute, you will see a red warning.

Something has stopped the running job. It may be a server side issue (for example your hosting not allowing long running tasks) or an error.
In either case, you should cancel the job clicking on ‘Cancel job’ and retry from start. If the issue persists, open a topic on the support forum or email me: [email protected] (i will likely need your xml file(s) in order to check the issue).