Class 12-science

I think you should go for Science because it has more options than commerce.

Hello,
There are too many career options available for PCM+ economics candidates.
You can pursue BBA and MBA or you can go for a law course. Engineering, BA in economics, B.Sc, CA, CS, Army course, fashion designing, etc. are few of the good options.
There are unlimited fields for a PCM student. So go for the career in which you have more interest
I hope it will help you.
Best of luck.

There are various exams like AIEED, UCEED, etc. through which you can get admission in a good college for fashion designing course. Their forms will be out in the month of October or November.

No, its not all necessary on rely on coaching for 11th and 12th, you can prepare at home. You just need to dedicate yourself for regular studies. Daily revising the concepts and giving importance to difficult concepts as per you. Perform well for periodic school exams. You can score good with self study alone.

You can consider the below mentioned Bachelor courses:
1. B.Sc.
2. MCA.
3. BCS.
4. B.Pharm.

Yes, you can go for integrated MBA in which you will learn BBA+MBA (5-year course). If you want to do MBA then go for it, otherwise do Bachelor's and then MBA because you can change your stream in between the courses.

It is not possible to become the same after 12th. You must pursue Bachelor's degree in automobile engineering or other equivalent course.