1. Same way it is calculated for resident husband here in India.
2. Only difference in NRI husband case is exaggeration of non-residents income by resident spouse and since most cases NRI husband gives PoA to service his version the lower Court initially favors resident spouse version on NRI husband’s income and then Appeal and set-aside is what follows.
3. You give your expense, liabilities statement and press for her side to also give the same and then use factor of her education, ability etc. to counter maintenance claim. For this part understanding read various past discussions here on ‘no maintenance to able bodied wife’ postings.