Yes. The system will either take payment at the end of the month if your customer has signed up to Go Cardless or it will send them a statement.
You can select from various styles and colours, enter your logo in the setup and it will appear on the invoice.
Yes, you can void an invoice and it will not appear in your sales figures.
Yes. Save as a Draft, it will not be sent to your customer until you are ready.
Yes, the invoice will queue on your phone/tablet and automatically download when you get a decent signal.