Paperwork and payments for a gite complex?

I run a gites complex in France with my husband and have a few questions:

1. I keep a basic spreadsheet of all our income, do I need to produce an invoice for every booking?
2. Sterling income goes into a private bank account in joint names in the UK and Euro income goes into our joint personal French account. Is this OK or do I have to have a business bank account?
3. You have advised that receipts of costs should be kept, I have a file full of them - do they need to be recorded in any other way?
4. We’ve had the business for 2 years and have just become aware that we should have registered as meubles de tourisme to benefit from a higher turnover and lower cotistations. Am I right in thinking that we must stick to a turnover of maximum €32,600 and not €86,000 until our rating has been confirmed by the profecture?
5. We have recently been rated as 3 stars, once the certificate comes through from the prefecture what do I need to do to benefit from the higher turnover and lower cotistations?
6. Having been rated does this restrict how much we can charge?
7. Until now we have been paying 21.3% on all turnover, we serve food on request and I am wondering if we should only have been paying 12% on the food sales?
8. For sales in Sterling, when it comes to working out my cotistations what exchange rate should I be using?