Aviation

B.Com. is a graduation degree course, and Cabin Crew course is a professional training. It will not add to your education, but it will help you get trained for a particular job role.
Hence there is no harm in doing both simultaneously.
For your convenience, I've listed below the general guidelines and requisites for becoming a cabin crew member.
In general, candidate's profile for freshers for cabin crew is as under-
Age: Between 18 and 27 years
Minimum Height: Men - 170 cms and Women - 157 cms
Weight: In proportion to height
Educational Qualification: HSC (10+2). Candidates who are appearing for their HSC examinations can also apply.
Physical features: Pleasing personality, clear complexion (scars, pimples and blemishes not acceptable) and good eyesight
Marital Status: Unmarried
Language skills: Fluency in English and Hindi. Proficiency in a foreign language will be an added advantage.
Interactive skills: Excellent communication and good interpersonal skills
Nationality: Indian citizens only
Passport: Must possess a valid Indian passport or should have applied for a passport
Mandatory Documentation: Must possess a Pan Card and Aadhaar Card
So that becomes very clear that it merely requires some grooming to get the job of a cabin crew. They don't demand much from the candidates.
You should be interpersonally sound and capable to handle people from different cultures.
Cabin crew is the face of the airline.
Foreign languages like German, French, Russian, Arabic, Chinese and Japanese, etc. can allow you to get an edge over others, as this allows the airline to roster you on routes where such languages are spoken.

Your Mechanical degree will be an additional qualification for you, although it will not be used for any privileges for issuing your CPL.
For becoming a commercial pilot, there is a specific eligibility criteria, which you should first be aware of. This is decided on what subjects have you taken in class 12th. It requires 50% in PCM to be a pilot. And even if you have not opted for the same, then you can appear separately for these subjects and become eligible.
Further, you should be aware that you are medically fit to be a pilot, so I would suggest you to visit http://www.dgca.nic.in/medical/medical-ind.htm and go to the Class 2nd examiners tab to find out doctors who will examine you for initial fitness. You can visit any doctor from the list as per your convenience.
Once you are done with Class 2nd medical, find out a suitable flying club for you as per your convenience. You can fly in India or abroad. I would suggest you fly in India. Besides finding the club, be aware that you will have to appear for:
1. Air Navigation
2. Aviation Meteorology
3. Air Regulations
4. Aviation Technical
5. Aircraft Specific
6. Radio Telephony
Here, 1-5 are conducted by DGCA and 6 is conducted by WPC. Prepare for these subjects and appear, as exams are conducted every quarterly. For preparation, flying club will help you or there are private instructors available in metro cities as well.
You will have to fly for 200 hours+ clear DGCA and WPC exams + clear Class 1st medical, then you shall get your CPL.
The next license is ATPL, which you shall be able to apply for at once.
You will then have to probably fund or self-sponsor your type rating on whatever fleet you are selected in an airline. Then, you finally get a job as a pilot.
I hope the process is well explained to you. CPL is an expensive affair. It might cost you around Rs. 18-20 Lacs for flying + DGCA exams Rs. 500 each exam + medicals for Rs.10,000 + endorsements and license issue fees around Rs. 25k + type rating around Rs. 15 Lacs. So, decide wisely before you enter the field.