@Ashu
No problems with warranty at all. Its not Apple for nothing.
Since the discount comes 'with' the purchase of a new Mac, I suggest you buy it when you buy the Mac, wherever that may be.
And I fathom the pricing is higher in India than US? It might not be much from Apple, but there are no reasons you should not get them together.
Also, you might want to use the MacBook with a larger display or TV. For that, you have the choice of buying Mini-Displayport to VGA or DVI adapter. I suggest DVI, since VGA is struggling nowadays, unable to go higher than 1920x1080. You can drive upto 2560x1600 resolution screen with DVI. (I am not sure, but I guess you will need a dual link DVI setup to go that high).
The adapter, sadly, isnt bundled. Apple probably thought many people dont use monitors with laptops at home/work, and kept that optional at 29$ or so.