Should I use AGESSA in France?

I am a music composer who earns money through commissions and worldwide royalties. At present these are all paid in the UK to my UK Limited Company at around £70,000 per annum gross. Expenses are not huge, say £10,000. There is one main client who accounts for almost half the income (mainly licensing), the rest is largely PRS (royalties) with a few commissions (TV companies etc.).

1. I have read about AGESSA (association pour la gestion de la sécurité sociale des auteurs), is this the best way forward for me when I officially move to France next year?
2. Does being registered with AGESSA preclude me from starting a EURL, SARL or indeed an EIRL business in France? (Can you see any benefit in any of these for a composer?)
3. Is there a danger I’d have to set up a portage salarial even though all my work is freelance?
4. Can this fact in any way justify (to the French authorities) me keeping my UK Limited Company active alongside my new French business? Most of my income is royalties for business activities that took place in the UK many moons ago.

I read elsewhere on your forum that:

When you live in France and your business activities take place in France… you must trade via a French registered business and pay your taxes in France.

I will be resident in France but still have a permanent address in the UK.