1. Income tax is payable on the net profit. It seems that the contract is related to the independent personal services. If you are working as an IT professional or other specified professional, you are required to maintain the books of accounts and get them audited. If you are working as a non-specified professional, you can take the benefit of presumptive taxation scheme u/s 44AD up to gross receipts of INR 2 CR.
2. As it is an independent personal services, status of individual will be considered and benefit of tax slabs will be applicable.
3. It seems that it is an export of services. You are required to obtain GST registration once the gross receipts exceeds Rs. 20 lacs. Apply LUT after obtaining GST registration for exports without payment of taxes. Entire process is online. File the GST returns quarterly. Collect and retain FIRC from banks for foreign inward remittances to take the benefit of exports.
You may consult telephonically for further discussion.