I would start Pujara at #6, use Kohli at #3 and Sehwag to #5. That way you can follow Sehwag with a more responsible player. When Tendulkar retires, then Kohli would drop to #4 and Pujara up to #3.
Anyway, Sehwag will be fine as opener on home soil but for overseas Tests he should be moving down to shield himself.
I personally think Pujara will make a better #3 and should be started there, but we'll see how Kohli and Pujara go about their business, that #3 spot is theirs for the taking really.
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Have a look at this, from about 2 and half years ago.
Virender Sehwag "would love" to bat at No.4 | Cricket News | Awards 2009 | ESPN Cricinfo
Senior batsman wants, senior batsman gets, at least that's how it works India.