Thickness of final coat for terrace

[mike.m]

We have a largeish area of terrace which has been left unfinished . The surface is a good quarter metre of mixed stone which has been well compacted . I'm now planning to lay a final layer of limestone ( 10 mil  diametre ) and am wondering :

1. How thick should this coat be ?

2 Is it too late at this stage to insert a geotextile layer ? If not any thoughts about the best / cheapest material and who might supply it ? Would it be suitable for sections where there is vehicle passage .

 

                                          Many thanks