Science

Yes, PSG is a very good option to pursue biotechnology.

Both are best.
It depends on you that what you want.
If you think about secure scope, then go for general B.Sc.

Life science has huge syllabus, so it is very difficult to complete full syllabus. Hence, once try to first find the subject in which you can score well, and you are good at, also I would suggest you to please join some coaching institute for the same, as they provide you the best of ideas and tricks to crack NET.

AIIMS is the topmost college for MBBS, then you can go for NEET colleges such as Moulana Azad, Lady Hardin Medical College (only for girls), VMMC, UCMC ( New Delhi), BJMC-GUJRAT, Grant Medical College (Mumbai), PGIMS- Rohtak (Haryana), SMS Medical College (Rajasthan). If you can't score well in NEET exam, then you can go for private colleges. Except MBBS, you may also go for BDS, BHMS, BAMS etc.

Both are equally good streams and having equivalently good job opportunities. Science will open opportunities in the field of IT, Aeronautics, Automobile, Civil, Agriculture and many more. Commerce is more related to core business sectors and is evergreen like most of Science subjects. Commerce will open opportunities in Finance, Accounts, Banking, Insurance. In the current scenario, education quality of Science is better as compared to commerce. IITs, IISC and NITs are top institutes. India is still developing and much scope of advancement in newer technology. So, lot of opportunities are yet to come.

Kendriya Vidyalaya, DAV, etc.
These schools are reputed and provide good education also.
Delhi public school is also good in terms of education and discipline.

You should opt for B.Sc in chemistry.
Good luck.

Which stream did you opt for in class 12th?

B.Sc in biotechnology would be a better choice since microbiology is a part of biotechnology.
Good luck.