Hi,
Are you using any theme for virtuemart?. Or default joomla 3 template?. Also, are you using one page checkout?. or multi step checkout?.
For invoice generation, there is a component com_invoice. Are you using this?.
Do you want a separate extension/plugin to achieve those?. Otherwise we will need to modify the existing template/virtuemart files.
You mention, you can provide more info about this project. More explanation will be helpful to understand the complete task.
Thanks