Moving from UK to France and Managing our Tax Liabilities Properly

We would be really grateful if you can help my partner and I with some initial online advice. Hoping you can guide us by letting us know how things work prior to getting to France permanently. We have been living in the UK until now, but plan to emigrate to France in 2018/19, making it our primary residence, before Brexit. 

We plan to become French residents and eventually French citizens.

My civil partner and I bought an agricultural property in 2014 in Limousin, and would like to develop it as an organic farm. We intend to register it as such with the Ministry of Agriculture. The farm is a smallholding (approx. 9.5 acres). We will be cultivating organic fruit and vegetables, and selling added value products e.g. jams, botanical drinks etc selling at farmers markets and restaurants and possibly a CSA scheme. It will have animals, as part of the farm, but not animals for breeding or sale.

Questions we have :

1. Property sales/purchase – we are selling our flat in the UK; this will enable us to invest in the farm. We plan to buy a small house in the UK to rent out, possibly via a managing agent – are there any tax implications in the sale we need to be aware of?
2. Tax on rental income - Also, if we rent out the UK property, and receive that income whilst we are resident in France, what is the level of tax we might expect to pay on that? What if the rental income is sent to us via a managing agent for the rental property? Does that increase how much % of tax we would have to pay?

We have other legal structure questions but will label those as such when we ask them. Forgive the repetitions in that question with some of the above details.

Thanks in advance.