Getting 55 percent of Brookhaven residents to agree to form a city — the smallest margin in the metro Atlanta cityhood movement — may have been the easy part.

Still looming is how the north-central DeKalb County city will set itself up, even though it opens for business Dec. 17. Gov. Nathan Deal has yet to name the five-member commission tasked with helping shepherd that process.

DeKalb, meanwhile, has yet to plan how it will handle losing as much as $40 million from next year's budget from the creation of Brookhaven and a likely annexation into neighboring Chamblee. The best guess is the hit could mean a 5 percent reduction across already-stretched departments countywide.

Both sides insist they will find the answers. But the uncertainty raises questions about what will happen not just with county taxes — which could go up — but with services for both the city and the county — which may not be what people expect.

"Will Brookhaven want its own police force? If the answer is yes, how will you prepare for that?" asked Oliver Porter, a consultant who helped launch Sandy Springs in 2005. He has since worked on the creation of Johns Creek, Milton, Chattahoochee Hills, Dunwoody and, now, Brookhaven.

Those earlier new cities all opted to outsource nearly all government services to private firms while keeping only administrative and public safety jobs as part of the official government.

That system requires at least an interim city manager to oversee hiring and planning as well as task forces to handle bids from the private firms. So far, Brookhaven has only the task forces, which have done limited planning.

Part of that may be because advocates for Brookhaven worked on their effort for just a little longer than a year, unlike counterparts in Sandy Springs and Dunwoody, where the efforts took three decades and three years, respectively. Those two cities also started planning as more unified communities, with 94 percent of Sandy Springs voters and 81 percent of Dunwoody voters supporting cityhood.

By state law, cities are required to provide at least three services. Brookhaven proponents cited four they want to take over from DeKalb: police, paving, parks and zoning.

But unlike Sandy Springs, where zoning was the priority, and Dunwoody, where most voters voiced support for police, Brookhaven did not single out any one service that will be its first order of business. Brookhaven advocates simply said they felt local government could handle services better.

"All of that work was already happening in the other cities," Porter added. "The implementation timeline does give me concern."

In fact, readying for DeKalb's second new city in four years means a packed calendar for the next 100 or so days:

-- Brookhaven voters pick among 22 candidates for four City Council spots and four candidates for a part-time mayor's job on Nov. 6.

-- The runoff election, likely given the sheer volume of candidates, is Dec. 4. Two weeks later, the city officially begins operations.

-- County department heads are to submit their budget requests to Chief Executive Burrell Ellis by the end of August. Administrative budget hearings begin later this fall.

-- Ellis must present his recommended spending for 2013 by Dec. 15. Always a speculation given that revenues don't come in until Dec. 31, next year's budget will include even more guesswork since DeKalb won't know how much cash to set aside for the services Brookhaven could take over once it's up and running.

"There is really no one to negotiate with until November, and we don't know how fast they can speed up some of their services," said DeKalb Chief Operating Officer Richard Stogner. "There is even a question mark as to what all the services will be."

J. Max Davis, the president of Brookhaven Yes who is now running for mayor, said the priority will likely be a police force. But even with that, a timeline is unclear.

Dunwoody had its force up and running in record time, in about four months — meaning it still negotiated and paid for DeKalb protection for the first quarter of its first year.

Davis said cityhood proponents have set up task forces to look into those questions but like most residents in the area, are waiting for direction from the governor's commission.

"There is a sense of urgency, but we don't feel we are behind," Davis said. "We always knew we would use DeKalb County for a while. It's not going to happen overnight."

Action will require more than just those running for office. Brookhaven will need residents to get involved in planning but also those willing to serve on city boards that must be set up, such as a planning commission or zoning appeals board.

Joan Dillon, an attorney who was won over to supporting cityhood over the argument of closer community service, is among those who plan to volunteer. She encouraged neighbors to support incorporation and feels she has an obligation to see the process through.

"I want to make sure it works," Dillon said. "The timeline is tight, so we have to work together."

What direction the city takes is likely to rest on the outcome of the election. A handful of vocal opponents of cityhood are among those who have thrown their hats into the ring for office.

If people with those mindsets win office, a new Brookhaven council could in theory decide to stay with DeKalb on most government programs.

The only requirement for cityhood is Brookhaven provide three services, out of more than 40 possibilities that range from big-ticket items such as a police department to more mundane doings such as mapping services or code enforcement.

"I think at the end of the day, it will be very difficult for the city not to provide a Brookhaven police force. That's what people were expecting," said Jim Eyre, a member of No City Brookhaven who is running for the council seat in the Ashford Park area.

"At the same time, I don't want us to trip up just because we are in a hurry to call them Brookhaven services instead of DeKalb," he added. "There's a lot we need to answer at this point."