Setup your top level menu. You need to specifically add the categories and subcategories to your menu, they will not automatically be added.
Input your address. This will not automatically be displayed on your shop. You can set another address to be displayed on the site.
Modify your state code in the GST setup under taxation (default is Maharashtra). This will help the system correctly charge CGST, SGST & IGST.
Add a few of your products including at least the title, one image, a small product description, and its price. The title and the description is important for search engine optimisation.
Setup your shipping according to zones.
Setup your payment gateways.
Ask ShopShastra helpdesk to check the setup of your shop at this point
When they give the go ahead, upload the remaining products. If you have many, ask the techdesk for tools for bulk upload of products.