On or before the first day of February of each year, each officer and department head shall submit to the Mayor a complete statement of the financial needs and expected revenues of his office or department for the next fiscal year. The Mayor shall assemble all the statements so submitted and prepare for the Council a budget proposal for the next fiscal year. Such budget proposal shall be presented to the Council at its first regular meeting in April. The proposed expenditures set forth in such budget proposal shall not exceed the expected revenues of the city for the next fiscal year by an amount greater than the expected unencumbered funds, not transferred to any special account under authority of Section 7.7 of this chapter, remaining at the end of the current fiscal year.