BBA

Hi Rohan,
If you have done any Diploma course, then you can surely get admission .

In BBAU, admission is taken on the basis of both firstly merit list, then counseling will be taken.

I think, it must be opened. Kindly contact the particular college in which you wanted to take admission.

MATHS - I would refer R. S Agarwal of Class 11th and 12th. Just stick to basics of the chapter in syllabus. Also, go for quantitative aptitude of R. S Agarwal.
REASONING - verbal and non- verbal aptitude of R. S Agarwal, and also solve CLAT materials for reasoning section.
ENGLISH- Go for Arihant and S. chand materials and also solve Oxford's materials.
G. K and business affairs- read newspapers and magzines G. K today will be preferable and play online quiz on current affairs on quiz today.
Practice as much questions as you can and stick with basics especially in Maths and English and there you go.

It entirely depends on what exactly are your farther future goals. But, I personally feel that B.Com would be better.

B.Com has better scope than BBA. B.Com will open the gates into financial roles in organizations, which are more available as compared to business roles. Finance also opens career options in markets as risks, insurance and credit analysts. B.Com along with MBA in finance will have better career prospects. BBA on other hand is a professional degree that will only lead to MBA until you plan to do CA, CFA, CMA or CS which are possible with both degrees.

Anil Surendra Modi School of Commerce,
IIBMS - Indian Institute of Business Management
For more top universities list you can visit following link-
https://www.shiksha.com/bba/ranking/top-bba-colleges-in-Mumbai-all/93-2-0-10224-0.

According to me this college is good choice because here placements are good.

Go for SAP course, since now a days SAP is the mostly used accounting software it's far better than tally, course of tally is now wasting time but if you do course of SAP its advantageous when you will go in industry for job as well it will add up value to your current profile.