[jituc]

Do not worry too much, for now you do not even need gst registration.

Taxation is mostly based on your and your customer's location. If you are in India and customer is outside of india, you are exporting service you dont need to pay Gst, its exempt. If customer is in India and your yearly turnover is less thN 20Lac you still do not need Gst. Its complicated. Just build your Saas and get bootsteaped to 10L revenue, then visit any tax consultant.

In case of starting a company in USA use stripe atlas with virtual address, and get an agency who files taxes for you, consoder total yearly cost to $15k.