Any realtor can guide you through the process, it is best to have a realtor who's area of expertise is in teh area you wish to buy.
Yes, you need a realtor for the offer and a closing agent for you closing, which often is an attorney. You may want to get legal and tax advice from a local attorney and accountant so that you know your tax liablities in the US. Most realtors have contact for you, as I do.
I would be glad to assist you, the areas I specialize in are Miami Beach, Aventura, Hollywood and Sunny Isles.
Feel free to contact me directly with any questions, I have worked with buyers from out of the country very frequently and will have the answers you need for a smooth transaction.
South Florida Brokers