Just read through supplementary material and relevant cases for IDT and work out problems in RTP. Keep reading and revising it till the exams. Definitely study RTPs for Nov 11 and May 12.
Study wealth Tax, Amendments and select Cases for DT. apart from that assessment procedures, Capital gains and PGBP are important. (DT is a tough nut to crack. can't really strategise much).
For Costing concentrate on OR (LPP and Network especially) and in costing quickly finish off Activity Based Costing, Budgeting then proceed to big chapters like standard costing and transfer pricing. last 2 days before exams keep reading theory from past papers and revising concepts in all chapters. work out a mock test.
For ISCA- study practice manual and search for Mr. BVN Rajeshwar 's important questions and study those questions. then proceed to detailed study. BCP/DRP, Risk management, ERP are pretty easy. SDLC, Testing of controls and IT Act are important. You'll definitely be able to finish studying ISCA within this week.
Last thing.. take it up as a fun challenge.. Be in the present moment and now is not the time to think about the past or future. Have a lot of fun learning... Wish you the best..:)