Both of these features are planned, allow me to elaborate.
What we intend to do here is add a checkbox to the “Log a payment” dialogue, this will allow an email to be sent to the client which is based on a predefined template. This is a pretty simple implementation for us and should be ready in the next 6 weeks.
We are just in the process of beta testing a new invoice style gallery and editor. Once these new features have bedded down we will allow custom styles to be assigned to specific invoices. It’s hard to put a time-frame on this but it’s likely to be within the next few months.