Moving to the south of France

I've been a carer for my parents for the last few years. Dad passed away March 2016, Mum still with me but one day I shall be alone. I have just had my 60th birtrhday. I would like to spend my time in the South of France where the climate is warmer and the sun brighter. I hope to spend my time as an astronomer. I'm looking to find a location, with zero light polution, so no cities or towns, something rural. Lakes are good, Somewhere I can put a mobile home or leisure home, my needs are few, I don't need a big house. Do I have to register full time in France, can I stay for long periods of time, I have a rented property in the Uk, I would like to buy something in France. What should I be considering. I do not need to act now as my mother is still with me but she will have to go to a home soon.