Hi Saurav,
1) You can enroll for CA by making registration with ICAI in CPT course. As shown from yours marks you are very intelligent . But as far as CA registration is concerned ICAI not make any difference in 12th pass student or graduate or postgraduate student and all have to clear the three stage of exam. viz. i] CPT ii] PCC/ IPCC & iii] CA Final. Till 2006 graduate student can make direct enrollment in 2nd stage. But now this scheme is withdrawan by ICAI. so now you can enroll for 1st stage i.e. CPT . and as i know enroll till june so that you can get earliest attempt of CPT Dec. 2010 , i am not sure regarding date you can confirm with ICAI website and the fees is nominal i think it is around Rs. 6500
2) Your articleship will be started after you pass CPT / 1st group of IPCC so till that you can completed any number of courses but as as soon as your articleship will commence only 1 course along with ca is allowed.
And in my opinion if you will join ca couse there is no need to join M.com and after passing 2nd stage you can get M.com degree after giving exam of IGNOU in 6 months since ICAI & IGNOU has MOU in this regards.
3) so go for LLB along with CA but remember one thing you can clear CPT & IPCC in 1or 1.5 years but duration of LLB course is 3 years and if your college timing in LLB is in between 11 am to 6 pm you can not start your articleship .