Applying for a position as an unlicensed Chief on a tug all you really need is an MMC with OS/wiper. Your foreign license, STCW Certs and experience are what will impress most employers.
That said, I suggest that you apply for and take all the exams for QMED-Any Rating. I think the exams will be very similar and you can breeze through all of them in one week. You might as well get all you can.
If you only get oiler, some employer may wonder why you don’t have the other endorsements. A company hauling frozen fish might like a reefer endorsement. A company having electrical problems might like an electrician endorsement. Some HR girl screening CVs might be impressed by junior engineer.