You can actually take the training online now through an internet course, then go take the Federal USCG test after the course. The course online is run by a company called Mariner's Learning Systems.
You will need a lot more than an alien license if you wanna be a professional guide; a marketing plan goes along with a real sense of being part of our community. An internship for a year or two with a real pro will not hurt.
The way most captains get their license is by going to either Sea School or Adams Marine. It is a course you attend. The course cost is anywhere from $450 to $600. You also have to have a certain amount of sea hours (time on a boat) logged to qualify for your license. You will also learn about the different requirements for fishing in Federal waters compared to fishing inshore or even nearshore.
There is also a medical test and your CPR and first aid course you have to take. The course is excellent for boater safety and more.
You also need the license in order to run any boat operation on the water. If you plan on running a business there are some other licenses you will need.
Realize, however, that getting a license (and even being a good and consistent and effective and friendly angler) is not the beginning of a successful business. A business plan is the beginning of a successful business.
Learn to do seminars; be kind to kids. But most of all, learn to market yourself. That's far more than I can cover in a short answer to a relatively simple question. You have a lot of competition out there and working as an intern for a great and established guide - and washing up after him or her - is way more important then the licenses you need to do it legally. A lot of specific information about what licenses you might need for what kind of operation you intend to run can be found on the FWC site.
Feel free to e-mail me for more direct answers to your questions..