Scope of total income and incidence of tax depends on the residential status of an individual in a previous year
1. Yes
2. Global income
3. Yes
Citizen of USA are also treated as resident of USA for tax purposes therefore tie breaker rule will be applicable to determine the residential status of a person. In India, tax period is financial year (i.e. from April to March) whereas in USA it is calendar year due to which there would be a difference in the reporting of income subject to withholding taxes, foreign tax credit etc.
Providing independent professional services from India to USA clients would also attract GST registration and filing of GST returns. Assuming your gross receipts from the services would exceed Rs.20 lacs in a financial year
Also you would be liable to pay Professional tax in Maharashtra
For detailed discussion you may opt for phone consultation