Accounting & Commerce

You have plenty of courses to pursue after 12th commerce like:
BBA
B.Com
Actuaries
Integreted Law
CA/CS/CFA
Mass Communication
Journalism
Business Analyst
and many more.
First thing, you have to do is identify your interest of subject or field and let us know for further guidance.
For getting good placement:
1) Improve your skills
2) Should maintain a good personality.
3) Vocabulary should be good
4) Fluent in English speaking
5) Know your strength and weakness
In addition to these, studying in a top rank college may count.
I hope this answer has solved your query to some extent.
Please feel free to revert.
All the best.

After 12th there are very few jobs available. You can join a BPO or work in a CA firm. You can also appear for government exams (clerk level).

If you want to learn about the commerce field then join a CA firm or if you want to do a job in the evening then you can join a BPO.

No, you can't because you won't be able to manage both simultaneously. It's better to focus on one thing that would be better for your future also.

You are advised to pursue either MBA or M.Com course.

It takes around 3 years and 6 months if everything happens well.