Receipts and Invoices for auto entrepreneur

I have just set up as auto-entrepreneur and one of my activities is running a mosaic group. My customers pay 30 euros per session on the day they come.

1. Do I have to provide a paper invoice/receipt to each client for each session? (I know some will say I don’t want/need a receipt, do I still have to make them one?)
2. Can I download an app on my phone to create invoices/receipts to email to them?
3. If yes, Do I have to keep printed paper copies of those invoices/receipts? Or is it sufficient to keep the information in the app?
4. If yes, Can you recommend such an app?
5. if no - I am aware of all the info I need to add to an invoice.  It seems very laborious to write all this info out for sixteen students every week.  Can you suggest a way to do this more easily?  ie, Is it possible to buy a pre-printed receipt/invoice book so that I only need to add their name and how much they paid?
6. If yes. Where can I get one (or what do I put into Google to find such a service?)
7. Can I create my own template and print my own basic invoice, then hand number them as I go?
8. Is there anything else I need to know about record keeping other than having a hand written book/accounting software which chronologically lists receipts and expenses?
9. Can you recommend cost effective software for this purpose? Or is it best to keep it in a book?

Many thanks