Congradulations for having a clear view of what you want. It is very important to have a clear view.
However while choosing the options for studies, it would be better if any and all the courses are choosen that are co-related.
For example MBA in supply chain and logistics may not that well be related with PGD in Maritime law.
If you are interested in Maritime law, focus on that. Choose the courses for higher studies related to maritime law and be an expert in maritime law. Target to complete LLM in Maritime law and if you still want to go a step higher, may be go for Phd in Maritime law.
Similarly if you are interested in Supply chain and logistics, focus only on that area.
With regard to your second question, if you should leave sailing or not. It is difficult to answer that in Yes or No.
You need to look for various factors. Do you have enough money to sustain while doing your higher studies? Do you feel sailing any further will help you gain more knowledge related to the area of studies that you have planned?
And few other similar questions.
After doing a good assessment of all these factors, you may decide if it is better to quit sailing now or not.
However just for MICS, I would not recommend quiting sailing. This is not a qualification but membership for ICS. The studies for this can best be done while sailing.
All the best for your future and feel free to ask any question that you may have for your career development.