If you are selected to Engineering, Don't look for Pre engineering courses during the free time. Its waste of time and you should be able to learn what is required in the university during the allocated time.
As your friends said, CIMA, CIM, HR, Management like courses will help you to broaden your knowledge in affiliated areas and you can be an effective engineering manager easily.
I don't recommend PMP without project experience. But improving English is a must. In addition, you can follow personality development programs Toastmasters is one of them. Or else look for a part time opportunity to work at least in Pizza hut, where you will learn what is the world is.