Some of your Questions:

About getting started

Do I have Codes Access and Ownership?
Any additional cost for domain and Space.?
How many days it takes to go live.?

About customizations

Does Nationkart design website as per my documents ?
Can I get design customized as per my reference ?
Is there possibly of custom or Add on requirements .?

Catalogue Management

How will I manage my products and Catalogue ?
Will Nationkart Upload or Manage products and inventory for us ?
What kind of Support does Nationkart offer ?

Third Party Services

How does Payment gateway works ?
How does shipping works ?
Graphics and Media designing ?