Your NRO current account will be maintained in Indian Rupees.
RBI allows repatriation of balances held in NRO current account up to one million USD or equivalent per financial year for bonafide purposes (For e.g. education, medical expenses, employment etc.) with documentation. However, Indian income earned in the current FY (like rent, dividend) can be repatriable as per the above criteria.
The minimum amount required to open NRE current account is Rs. 25,000/- or its equivalent in foreign currency. You would be required to maintain an Average Monthly Balance of Rs. 25,000/- only.
Average monthly balance is the sum of daily closing balance of all the calendar days in a month divided by the number of days in that month.