Voters will decide on March 12 whether to approve raising taxes through the city’s first Proposition 2½ override in a decade, with plans to help cover repairs to aging buildings and deteriorating sidewalks, and to accommodate rising student enrollments. The Board of Aldermen voted unanimously Monday to back Mayor Setti Warren’s proposal to place three override initiatives on the ballot seeking a total of $11.4 million in new tax revenues. Warren proposed the measures to help pay for $143.5 million in projects, including road repairs, salaries for four police officers and new teachers, and building renovations. If all three increases are approved, officials said, annual taxes on a single-family house with the city’s median assessment, $686,000, would go up by about $343, to $8,006. Supporters of Warren’s override proposal have formed a committee, called Building Newton’s Future, to encourage residents to vote for all three ballot measures.