B.Com study

Yes, you can. You can directly register yourself with the ICAI and give the exam of Common Proficiency Test (CPT). If you clear the same, you are eligible for the second level I.e. IPC without any kind of graduation.
I think I can write my paper for this question properly as I had started my CA course preparation just after completing my 12th exam even before the result of the same.
The answer to the question is YES as ICAI allows the students after passing 12th Std. for appearing in the entrance exam of CA.

b.com study with ca is not mendatory. for starting of ca the elegibility is to clear 12th  exam in any source , if you wish to start ca intermediate directy, then direct entry option is available for that has to clear b.com graduation . as per new mra the ca final clear student is also to be consider as a complete graduate . as per my view is it advisable to pursue b.com or any other acadamic course with ca examination.