Firstly, have you tried using the Automatic Credit Control feature in KashFlow? This will automatically send out remind letters for you without you having to do this manually. This can be accessed in Settings.
The second issue that you refer to involves adding multiple customer contacts for different purposes. This is a highly requested feature from our users but is not something that we are currently planning to implement.
The only solution to this at the moment is to manually adjust the recipient address when sending the quotation or invoice.