Under IRS regulations, an organization that is established to solely support a ballot initiative should be set up as a 501(c)(4) social welfare organization as opposed to: (i) a political organization, which primarily operates to influence candidate elections; or (ii) a 501(c)(3) charitable organization, which must have a charitable purpose and can only engage in a limited amount of issue advocacy/lobbying. The organization must obtain an EIN by filing the SS-4 and most apply for recognition of tax exemption by filing the IRS Form 1024.
In contrast, incorporation is governed by state law. Generally, I recommend incorporating as a nonprofit corporation (the term varies state by state) to take advantage of limited liability protection, although you should first confirm whether incorporating has any negative tax implications.
Keep in mind that, although the organization will operate as a 501(c)(4) under IRS regulations, many states require an organization that makes expenditures to influence ballot initiatives to also register as a political committee under state law. Registering as a political committee will then trigger the requirement to file campaign finance reports with the state, disclose contributions and expenditures, etc. Therefore, you should confirm whether Florida requires such registration.
I am in California, and if it is a state election in Cal. you can set up a PAC without being a (c) (4). In fact, with all the attention (c) (4)'s are getting now because of the IRS so-called "scandal" you may want to avoid that route. You should talk to a Florida election attorney before going any further, to be sure you are in compliance with State and Federal law.
This response is not to be construed as establishing an attorney-client relationship, and provides general information on the subject at hand only.