Alot of questions here
http://www.subsim.com/radioroom/showthread.php?t=111509
When you complete task No. 1 you are free to sail virtually anywhere and engage shipping. You do not have to stick around the marshells. Once youve sunk 10K (I think) of merchant shipping you will fullfill the requirements of task No. 2
Your other questions I dont really know as I have not experienced this myself.