UK Residency and UK Limited Company

My husband and I would like to protect our position before 29 March, and are considering that one or both of us should become French residents. We have had a house in France since 2000 though, to date, have not lived in France for more than 183 days in one tax year.  However, my husband has spent close to six months in France in the last year.

• We are currently negotiating to buy an adjacent property which we would convert into gites -  likely to take a couple of years to achieve.  We could do B&B in our French home, but would not expect to make much income from this in the near future.
• We are both 62 years old with a UK limited company.  We pay ourselves small salaries and take dividends. 
• We will have the UK state pension when we reach 66.  We have a UK property which we may rent out.
• We are weighing up whether to start a business in France or maintain the UK company, or do both.  The work we do is mainly carried out online, and all of our clients are UK based.

I am investigating whether I can get Irish nationality, though proving that my grandmother was Irish is more challenging than I expected.  So, this remains a “nice to have”.

Current thoughts are - my husband registers as a French resident before 29 March, and we maintain the UK company.  In the event of a “no deal” Brexit, we both become residents before 29 March.

My immediate questions are:

1. Would it be possible to set up a business related to gites/accommodation before the 29 March deadline and would the costs outweigh the benefits?
2. What proof do we need of residency?  Is one supposed to wait until after one has stayed in France for 183 days before registering, or can one do so immediately?

Looking forward to receiving your reply.