Mathematics 3 or M3 in Engineering is a bit complicated but it can be explained. To tackle this subject, find a proper coaching centre to help you get accustomed to the syllabus. This will ultimately help you understand the concepts and techniques.  Gadge Nagar is known to have good coaching centers. After learning the concepts in the class it is your duty to practice them for at least 1 hour. SGBAUs syllabus is comparatively easier to manage and complete, so do not worry as you will be able to score better than the passing marks.

Probably not but it may be useful if you want to be a professor, and should prepare yourself to do a Ph.D. from a more reputed university. BE will help you understand the theory which you can ten implement practically. ME or M.Tech is basically for shifting to the teaching line. Though there are some specializations that will equip you with deeper technical knowledge.  During placements, you will have an edge over BE candidates. Students graduating with ME or M.Tech generally go for Research and Development.  Post Graduation has an advantage but for a corporate job, being a BE or B.Tech graduate, you can also apply. Studying 2 more years is a choice that varies from student to student. There is no right answer so, choose to do whatever you feel will be suitable for you.

Sant Gadge Baba Amravti University(AGBAU) is an average university in Maharastra. Colleges such as Prof. Ram Meghe Institute of Technology and Research and Shegaon College of Engineering have a good reputation and offer decent placement offers.  If you have better PET results or JEE scores, you can get better options than SGBAU.