1) Not sure how long the RTR results are valid, but the RTR License can be lifetime. But I'd suggest you pass your RTR and the DGCA exams and only then return to the US for your IR and CPL; in all probability, you'll save tons on recency.
2)Part 1 involves making and receiving radio calls with ATC (the examiner). But the answers are extremely rigid and I suggest you go for classes
3)Haven't heard about this. As far as I know, CPL holders have tow rite Comp. and Regs, and non CPL have to write Nav, Met and Regs.
4)His classes typically start 15-20 days before the examination dates. His no. is 9433044765
Hope it helps