Question 1:
They can be placed anywhere in FSX. Either at your current location or at a specific coodinate (Latitude, Longitude or a specific waypoint). Just make sure it's on the water.
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Once you postion your fleet there is a feature which will tell you where it is in relation to your aircraft's position.
Question 2:
You control the size of the fleet and the course. There is a pull-down which is installed on your modules tab which will give ou all the options. Make sure you don't set a course that will have you beaching your fleet!