Q.compost mix for Ficus trees
What compost mix is best for Ficus trees? Mine desperately needs repotting. It is now sitting on a 5-10 cm bungle of roots under the pot. How brutal can I be with cutting roots to get it out of is current pot and also to give the roots some freedom to grow new ways?

Ficus do grow quickly!
Select a new pot size 1 or 2 sizes larger. I personally would not trim the roots, just gently untangle them and open up the root system.
Here is a great link to get you started.
https://www.gardeningknowhow.com/houseplants/ficus/ficus-tree-care.htm
https://www.gardeningknowhow.com/houseplants/hpgen/learn-more-about-repotting-houseplants.htm