The Merchant Marine is divided into roughly two camps: The Deck Department, which is in charge of navigating and driving the ship and the Engine Department, which employs the engineers who keep the machinery turning for the Deck Department.
The Engine Department is not in charge of navigating or driving the ship, so you don't need to worry about purchasing sextants, GPS, and all that navigation crap.
The standard off duty uniform is usually khakis, and while you are working in the Engine Department, a boiler suit (coveralls) or some other casual clothing which can get dirty is acceptable.
It's too bad you've already gone thru a BSME program and now decide you want to be an engineering officer. There are schools where you could have trained to be a marine engineer from the get-go, places like the Merchant Marine Academy, SUNY Maritime, or the Mass. Merchant Academy, all of which award degrees, provide opportunities to work aboard ship while in school, and help you find a job after graduation.
You only need to take the FE if you want to become a Licensed Professional Mechanical Engineer. The licensing requirements to become a merchant marine engineer are a bit different.
As it stands now, you'll have to start at the bottom and get your seaman's documents, starting with the Oiler/Seaman Wiper card. You should contact the nearest office of the US Coast Guard or check out the website for the National Maritime Center at
for more information.