MHT CET

Yes, CET is enough to get admission.
Other than this, you need to score minimum 60% marks in your 12th.

With 90 marks in MHT-CET, you can't get in such colleges. class 12th marks don't play any crucial role in getting admissions to engineering colleges, but CET marks are important and it should be a minimum of 150.

Yes, you can go through college predictor.

Yes, you can do LLB course after B.com. The duration will be of 3 yrs.
The eligibility criteria for LLB course is that one should have B.A/ B.Sc/ B.Com degree with minimum 40% marks in aggregate for general category and 35% in aggregate for SC/ST students. But, you have to pass the entrance exam and personal interview.

Hello Sohan,
Check here for more insights:
https://www.google.co.in/url?sa=t&source=web&rct=j&url=https://www.shiksha.com/b-tech/resources/mhcet-college-predictor&ved=0ahUKEwilroj0qOnTAhVMMI8KHexzBbYQFggdMAA&usg=AFQjCNE0yQCarH8fgLECdumzy3J65y6ptw&sig2=ysE4Gyj6eW6cRjEIv-T7yQ

MHCET is all you need. No need to fill so many forms. However, in case, you didn't get good rank in MHCET, then you have to go for Management quota or deemed universities for which, you need to apply separately.

PUMBA (University of Pune), Indira Institute of Management, Indira School of Business Studies, MIT Group of Institute except MITSOB (PGDM) Singhad Institutes and Balaji Institutes (PGDM).