More than a third of the override, or about $4 million, would be spent to hire new staff, including 51 teachers and aides, and four fully-equipped police officers. The balance would fund road repairs and modular classrooms.

Mayor Setti Warren has campaigned relentlessly for the package of three tax increases facing voters in a special election March 12, saying they are crucial to the city’s future.

But overshadowing Board of Aldermen meetings and community forums is the memory of the $191.5 million Newton North High project, which ballooned into the most expensive school in Massachusetts history.

“It’s a case of being once burned, twice shy,” said Alderman Ted Hess-Mahan, who nevertheless supported placing the tax questions on the ballot. “I’m not sure we have the right numbers yet.”

Coming up with accurate cost projections can be difficult when the buildings won’t be constructed for several years and the feasibility studies aren’t complete, Hess-Mahan said.

Warren administration officials stand by their early cost projections, however, and say that the money for buildings and staff should help the city deal with its most pressing needs for the next five years.

“We thought we came out with solid numbers,” said Maureen Lemieux, Newton’s chief financial officer.

If voters approve all three Proposition 2½ overrides — which would raise the annual taxes on a home with the city’s median assessed value by $343 — officials will ensure that they stay within the projected costs, Lemieux said.

Two of the proposals are debt-exclusion overrides to pay for new Angier and Cabot elementary schools, costing up to $37 million and $47 million, respectively; the resulting tax increases would last only until the construction loans are repaid, about 30 years.

Warren is also asking voters to approve an $8.4 million operational override, which is a permanent tax increase, to pay for Fire Department buildings, a bigger Zervas Elementary School, road repairs, new police officers, and more teachers and modular classrooms to deal with the school district’s growing enrollment.

The district’s student population has grown by more than 910 in the past eight years, and is expected to add about 865 more by 2018. While the district’s enrollment has not returned to the peak of the late 1960s, Newton has bucked the statewide trend of low student growth as more families move into the city, said Deputy Superintendent Sandra Guryan, the school system’s chief administrative officer. The district now has about 12,180 students.

Under the mayor’s plan, the additional tax revenue would be used to hire new staff at all grade levels, and to teach special-education students and English-language learners.

Fewer questions have been raised about the staffing proposals, as aldermen have focused on the building projects.

Some recent facility upgrades that have cost more than initially estimated, including at Day Middle School, Carr School, and the Oak Hill fire station, have added to concerns expressed by some aldermen, including Hess-Mahan and Richard Blazer.

But it’s difficult to get an exact cost for building projects, as expectations and needs change in the planning process, said Alderwoman Deb Crossley, who is an architect.

“Everything changes over time, as you get closer to the final product. As your design becomes more complete, the price becomes complete,” Crossley said. “The real question to the voters is, do you like the plan? Is the plan a good plan?”

Crossley said the city brought on experienced staff to oversee the building projects.

The estimates for the school projects are based primarily on what nearby communities have recently spent per square foot, with inflation factored in. For the Newton Centre fire station, a headquarters building, and a facility for the Wires Division, which are also part of the override, city officials relied on a more general feasibility study completed in January 2012 for the Fire Department.

City officials are getting close to figuring out detailed cost estimates for Angier Elementary School, and are working with an architect on a design. But Angier’s feasibility study is not expected to be complete until June.