Check out this template. I wonder if it might offer you a good starting point that you can adjust to your specific needs. Also, the Airtable Universe might have some helpful bases for you to copy or check out for ideas!
For your final bullet point, I would suggest using a form to send to clients. Their form submissions would populate into a table. You could use a 3rd party integration, or if you are on the pro plan, you could use the page designer block to create an invoice to send back to the customer’s email.