In principle SmartCity should be what we all strive for, using technology where possible to make life less complicated and more accessible. I don't think your problems/issues are new and a well thought out plan, segregation of duty and defence in depth should meet your needs.
Why would hacker hack you over any other government!!
You mention WIFI for example. What would the purpose of this system be, who would it be exposed to and why?
well, I'm just raising my doubts, as previously hackers have targeted multiple projects both on a large and small scale.
For example every Metro station is proposing free wifi and so are other hotspots to provide access to the public to the internet.
This system is exposed to public and hence black hat hackers. They can potentially use it to gain access to the main server