Having been through US immigration processes several times and used US immigration attorneys, my advice is to use the services of an attorney to file the application if you possibly can. They seem incredibly expensive, yet the alternative of relying on the random good will of a case officer to have had a decent breakfast, be seeing your application right before lunch, etc etc. seems to be worse. Trying to deal with US immigration processes alone is not easy. Processes and regulations have been in flux and increasingly confusing for the last few years. The questions they ask at interviews do not have the everyday meaning that a native English speaker would think. It is not a good idea to take anything at face value when filling out the forms or answering questions.
Before you speak to an attorney it is helpful to ask others you know who have been through similar US immigration processes about your questions and your situation. By asking others you will probably discover issues to ask the attorney about that you have not have anticipated. And this can help you to deal with the attorney efficiently. As in anything, the more knowledeable you are when speaking to the specialist, the more careful they will be.
US immigration decisions include discretionary judgements by each case officer. An experienced immigration attorney who deals with the particular field office or consulate that you are applying through will know the process, and the individual officers histories, so will be able to prepare you so that you understand the questions and can answer them the best way you can for the person handling your case.
Lastly if you use an attorney, you should still take resonsibility to check and recheck every document for typos and completeness yourself. The attorney's office provides expertize in the process and immigration office, but you know your own data and you will find filing errors that they miss that could derail or delay your application, and thereby cost you time and money. Neither attorneys nor immigration officers have much incentive to make their processes efficient.
I can give you a referral to my US immigration attorney is San Francisco, but the Miami guy sounds more relevant if he deals with US visas issued here. Most US county bar associations will provide you referrals to attorneys, and the initial consult usually costs something like $100 for 15 minutes of time when referred via the bar association. You could try calling the bar in the county you will be visiting. Having a local attorney on your speed dial may be of real help one day.
