B.Com

Hey,
Visit the following link for detailed information-
Ambedkar Law University- The Tamil Nadu Dr. Ambedkar Law University. So, yes, you can I enroll in PG Diploma in Maritime law.
https://www.shiksha.com/law/course/p-g-diploma-in-maritime-law-the-tamil-nadu-dr-ambedkar-law-university-dr-radhakrishnan-salai-chennai-260960

It won't be possible to get admission now. Admissions are closed.

Please see:
https://www.shiksha.com/college/wisdom-school-of-management-lucknow-48020?showAllBranches=1&q=Wisdom+School+of+Management&rf=searchwidget&landing=ilp

You haven't quoted your 12th marks without which one can't suggest you suitable colleges. Then also the best colleges for commerce are:
1. College of Commerce, Rajendra Nagar
2. Vanijya Mahavidyalay, PU Campus
3. A. N. College, Boring Road
4. B. N. College, Ashok Rajpath
Apart from that, many tier-2 colleges are there. For forms and admission procedure visit these colleges and ask from their reception or admission counter.

Yes, along with your diploma in engineering, you can take admission in open university for B.Com and can complete both the degrees.

That depends on your interest. Both are good fields if you were interested in commercial or finance side. Go for B.Com and if you were interested in business oriented studies, go for BMS or BBA.

Timing of B.com programme course is 9 to 1 pm. You can go for orientation and then you will get the time table.

You have to clear entrance exams like CAT or GMAT to get admission in a good B-school. So prepare yourself for the exam.