ALL About e-commerce operator under GST

I Request You to answer me the following questions.

1.Who is an Eco?

2. When is he liable to Register? ( 3 cases- supplier of Goods or services or Both) 

3.What are all the sales to be considered in Aggregate Turnover calculation of ECO?

4.ECO GST Liability ( 2 cases- 1) if Supplier through ECO is Registered ; 2.  if Supplier through ECO is Unregistered

5.GST Liability of person suppling through Eco ? ( Both registered and unregistered)

6. ECO- TCS Provisions.

7. What is the manner of collection of GST from supplier and payment to government?

8.What is ECO's GST Audit criteria?