Duplicating an expense is not the same as a repeating expense, as you noted, Roy. So, I think this would be a very good feature to add. A button at the top of an expense ('Duplicate Expense') next to 'Add Another Expense', or make the 'Add Another Expense' button into a dropdown button, would be a great feature to add.

Credit notes from suppliers are normally accompanied with credit note documents just as expenses are accompanied with invoices. This seems like a simple feature to add and would be a great idea.

This was marked as planned more than two years ago, and seems would be a simple and invaluable feature to have. When is it "planned" for?

When I want to send an email to multiple tenants about a single tenancy matter, I have to send multiple emails which takes more time, and the recipients are not aware that multiple recipients (other than just them) have received the email.  So, I think this feature should certainly be added for a better and more efficient user experience.