B.Com

Yes you can pursue MBA after B.Com. It is advisable that you pursue MBA in Finance after completing B.Com.
Look, if your aim is to do MBA, then no matter what you pursue in graduation, you will always be eligible to do MBA afterwards.
All the best.

Dear Prashanth,
You have not mentioned how many backlogs and what was your final year percentage. A few backlogs are okay and the pass percentage should be above 65%. You need an IELTS score of overall 6.5 with no band less than 6. You do not need your GMAT for Australia and you need the your academic transcripts, 2 letters of reference and a statement of purpose. The exact academic requirements will depend on the University you are applying to and will be given on their website. Ensure that you enrol for a 2 year duration MBA as anything of lesser duration will not get you post study work visa or points for PR.
All the best.

Yes, you can pursue B.Com after class 12th.

According to Indian education act-1959, you can not pursue two degrees simultaneously, because it causes extra burden on students (according to law makers). But after the recommendation of few universities, UGC has now granted the permission for students to get enrolled in two degrees (in same or different universities).