Yes. The system will will send a statement for them to pay
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 and automatically download / get sent when you get a decent signal.