The game can still transpose into a main line...

Yep: I would have played 5.d4 now. That is what a slightly unusual move order can do: bamboozle you into an uncomfortable line!

I know the Dragon Sicilian with Bc4, leading to the Yugoslav Attack, but not with Be2.

Castling is not "bad", of course. Before it, you must check that nothing more important needs to be done defensively, and you must consider your attack plans, remembering that often attacks are done not because you plan to "crush" your opponent, but you want to "control" him, limiting his moves to the ones that meet your attack. IF none of this happens, to castle is ok. In this case, black has nothing but simply developing moves, and white can well take the tempo to castle. The only downside (meaning "potentially dangerous moves", but not inmediately forcing) could be (maybe) Bh6, but it is dubious.

With this move, White is probably committed to playing a Closed type of Sicilian.

White gives up attack (self-blocking his lsb, avoiding the central tension on d4, etc.) in spite of a calm and controlled position. The downside is that now the dsb can't move without considering the weak b2, but white can afford Rg1 in the near future.

White hasn't really given up ideas of attack. We're into a Closed Sicilian, now, a slower type of game. GM Vasily Smyslov used to play this sort of thing.

As said, "the starting of a plan, but not compelling right now". White has plenty of time to shield the queenside (if properly met all future threats over there, and this can include Rg1, which is not a problem now that the K is securely castled Kside...).

Not necessarily, because without b7, white threats Bxc5 after the pawns are exchanged. Nevertheless, I would have gone h3 - preventing b4, that was the beginning of white's pressure on the black squares. But the text move imposes exchanges on d5 that distract white from his plan, unless he goes on with c5, followed by b4.

Not necessarily! Take a closer look at the position. White has moved all of her minor pieces - conservatively, yes, but solid and well centralised. She has also castled. Black has but two minor pieces in action, and is still a move away from castling. For this he has staked out some territory on the queen's wing. This pawn thrust is by no means a 'lost' tempo!

This gives white exchanges in d4, and he can almost force the exchange of your Bg7, unless someting dubious like f6 was played. Not completely sure, but this "solves" the tension and black has not an unbalanced situation into the central exchanges.

8...b4 was worth a look (9.Na4 Qa5 10.c3 bxc3 11.bxc3 cxd4 12.cxd4).

Correctly, she doesn't want his dsb being exchanged but for the Black's one.

Of course, if white exchanges, he just help you to develop. But look to 9...Na5 instead, with Nc4 to follow, and white has either to exchange it with his lsb or go Rg1 in order to defend b2, with pressure (if Nd4 goes away, Nxb2!, RxN, BxNc3, with advantage). And the Nd5 has not targets right now, it's just a piece needing defence from other pieces.

Correctly thinking in being able to move the Nc3 if needed (which is likely to happen if black goes b4 - Qa5...). On the other side, W's lsb was "byting on granite", essentially doing nothing. // Black's Ne5 "threats" the exchange NxB+. It makes white lose his B pair, true. It is easy for white to retake the B (he has QxN, NxN and -probably worse- gxN), and you have got ridden of your best piece to seriously make the threat on the long diagonal (Nc6-Na5, if I am correct, of course!). Black makes his own Bb7 work much better, threatening e4 (that's why NxBc3+, gxf3 should deserve a second look, while (NxBc3+), Nxc3, b4 and e5 falls, and if QxNc3 e4 is pinned against f5 or similar. White has this to think about when playing the B to c3. And all of it is prevented by Nd4, and if e5, the diagonal is blocked and white can concentrate on his Kside, making either Nxf3 or Qxf3 playable again. where d6 would have been strong for white. But that's assuming black goes Ne5 in the first place. I don't see any Qside attack from black going on, I expected here Na5 instead, again (I am just blinded by that move?   and white has to think seriosly about how to defend b2 after Nc4.

How about 10.a4, here? After 10...b4, 11.Nd5 looks pretty useful for White.

Well done Joe! Black's correct move here was 10...Ne5, which would have stopped White's threat.

I would question this move as it just blocks dsb's action with no threat to the opponent. Ok it is "sensible developement", but it must have some downside, is too passive. Hard to see when you're playing a much weaker opponent! I tell myself: "be aware"!   (Joe, I can't follow your line with the analysis board. Please review it...)

Moreover, the NxN option is not possible due to BxB, threatening the R... while Nd4 has nothing useful to do other that being taken...  

This should result in the loss of the Exchange - rook for bishop - rather than a piece.

Rc8 seems not to be the better. After 11...Rc8, exNf6, Bxf6. White has a powerful attack with Nd5. Multiple threats begin to appear in black's field. It's difficult to work out if he can survive or get some compensation. For example, if black tries to prevent the exchange of his strong dsb and plays Be4 or Bg7, white has Nd4xNc6, threatening Bb6... (after White plays NxN, both BxN or RxN have its heavy downsides.

11...Nxd4 12.Bxb7 dxe5 13.Bxa8 Qxa8 14.Bxd4 exd4 15.Qxd4 Rfd8, and White is the Exchange ahead - Rook for Bishop.