Hello David,
1. We don't offer an invoicing service so to speak, it's more a payment method and amount and you print the event details page which should have the fee on.
2. Certainly! by default it is a .csv
3. Yes, this is automatically built in and the event creator and send an email to all or some attendees at any point.
4. Not at present, we do have integration with Acymailing though. If you wanted to use mailchimp, then ideally use it on site registration.
Many thanks
Tony