The first step is to visit Greece and conduct a survey to ensure that the market exists as you say it does. Understand and identify the services it requires.
You have two major points in your favor: your credentials and a backer when you prove that its investment will pay off.
If the maritime business is, in fact, as limited as you think, your next move should be to make use of your contacts in Panama. They may know people in your field who can offer you advice or information or they could provide the names of companies you can contact. With your background, you should be able to locate potential users for the services you'll provide. Make a list of every possible user and talk to people who can help you clarify who the real end users might be. Once you've done this, you'll be in a much stronger position to convince your future employer of your mission.
To devise a marketing plan, begin by preparing a mission statement that clearly and succinctly describes the nature of the business, the services it will offer and the markets it will serve. A few sentences should suffice. Then, list potential groups of users or clients and describe the services you'd provide them. Make an inventory of these services and identify new ones that you may provide in the future. Determine your needs in terms of staff, expertise and costs. Next, spell out marketing and promotional strategies. The key to successful marketing is understanding why someone would want to use your services. Then identify and understand the competition to position yourself in the market. List and compare your strengths and the services you'll provide.
In addition, you'll need to establish marketing goals that are quantifiable such as the number of new clients you'd acquire, people you'd reach or the amount of income you'd generate. Be realistic and practical in establishing your goals. Monitor your results carefully to determine which strategies work best.
You may also want to visit your local bookstore or research online service for additional resources on how to write a marketing plan. You'll find an abundance of information on this topic.
A savvy company knows that it takes time to build a business and should be willing to negotiate some kind of payment schedule for you to allow you to earn a living while the business builds momentum. Show them you're willing to work at a reduced, but adequate monthly salary for some period of time. Then you can switch to a percentage of business profits down the road.