Your recurring invoices go out on their own.

No. There is only one invoice per subscription and per period, and a unique key in the database guarantees it. Even if generation runs twice, the period already invoiced is skipped.

It is not required. Without cron, due invoices are generated while a user allowed to create invoices is browsing Dolibarr. If you prefer generation at a fixed time, the dashboard shows the automation status and the exact crontab line to add.

No. The module suggests tiered reminders, at 30, 60 and 180 days by default, each with its own email template. Nothing is sent without your approval. From the unpaid screen, you can send reminders for several invoices at once.

It is flagged "PDF missing" in the log and on the subscription record, with a "Generate the PDF" button. Since version 1.4.1, if the PDF model of the template invoice no longer exists, the module uses the default invoice model, then another active model. A missing PDF is also generated when the email is sent.

The due date depends on the payment terms. You can choose them for each subscription, or impose one on all generated invoices from the settings, including a fixed day of the month such as "the 10th". The due date is recalculated before validation, so the PDF shows the right date.