As Black against closed games I always has been a true defender of  "Grünfeld style" against almost anything. So after 1.c4 I play1.. Nf6 2.Nc3 d5 3.cxd5 Nxd5 4.g3 g6 5.Bg2 Nxc3 (I use to play 5..Nb6 too but that's not so easy if White play with d3 Be3 Qd2 h4, waiting before playing Nf3, etc) 6.bxc3 Bg7 and after 7.Rb1, I believe 7..c5 to be fully playable despite the results in practice. I have played it 2 times against a 2150 average and none took the challenge of taking the b7-pawn, but that's of course the best move here, so I didn't had problems because I could play with ..Nc6 then with a normal development. So after 7.Rb1 c5, 8.Rxb7 is of course critical, 8..Bxb7 9.Bxb7 Nd7 10.Bxa8 Qxa8 and know 11.f3 or 11.Nf3 has both positives and negatives points. But both have light squares weaknesses, a weak a2 pawn, a not so good bishop c1, so I believe Black has to play some precise moves but can reach dynamical equality and at the end a material and normal equality. That's could be an interesting preparation and I am waiting to play that on a corr game to test the idea.

I disagree a little with Mnb, but also with the thread starter. I think e5 is not a good plan and furthermore I feel it looks more like a Grunfeld than anything else.
Imo a better plan is to push for c5. For this the knight needs to leave c6 temporarily and b6 is also needed.
Having said that, I dont like this line at all for black. If you want to play like this, why not do it with 1..e5?
Eg 1.c4 e5 2.Nc3 Nf6 3.g3 d5 4.cxd5 Nxd5 5.Bg2 Nb6 6.Nf3 Nc6 7.O-O Be7 is a line I like to play. 
And yes, before anyone asks, I am the kind of obnoxious recalcitrant patzer, who feels the dragon is so bad I even can play against it a tempo down.

Basically as you can see I am still trying to figure out how this opening works.

Can someone tell me the principal line for me to learn after Nf3.

Indeed I wouldn't expect Black to rush into playing ...e5 while White is playing Dragonish moves.

In positions of this general sort, it is far from unknown for White to play for d3 plus c4, rather than d4.  One book that I think may shed some light on this is Michael Stean's "Simple Chess."

I don't need a computer to recognize a Sicilian Dragon structure after Black has played ...e5. And in the Sicilian Dragon White usually does not play Nd4xc6.