CAT

Start now by solving 5 - 10 quants every day and read newspapers every day to make your vocabulary strong.
When you get into the 3rd year, start your full-fledged preparation by joining classes or solving mock tests.

Yes, you can join classes there. There might be some centres of TIME or CL. However, classes only provide the baseline for CAT preparation. Rest is completely your own hard work.
All the best.

Minimum 50% is essential to appear for the exam. Though all good colleges prefer a criteria of 60% graduation score.

As BITS doesnt focus merely on CAT percentile but sees the overall profile and SOP for shortlisting so to be on a safe side a CAT percentile above 80% will be fine.

There are so many colleges which offer MBA without CAT but that doesn't add value to your Masters and you may not get placed in a good company.

you should score minimum 90 percentile

yes you can apply for cat exam only if you have minimum 50% in graduation. 90 percentile is needed to get admitted in decent college

Probably not possible.You can prepare for CAT exam along with M.Com. Try to score well to get admission in a good B-school.You may pursue MBA/PGDM after completing your M.Com.
All the best.

Hi,
These are the entrance exams specifically for MBA/PGDM courses.
CAT-Common Aptitude Test
It is conducted by IIMs
CMAT- Common Management Aptitude Test.
Conducted by AICTE.
XAT- Xavier's Aptitude Test.
Conducted by Xavier's Institutes.
Most of the colleges accept any of these entrance exams for the admission process.