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The Open Sicilian is even more complex, in my opinion.

This is not yet an open Sicilian. It all depends where White plays his d-pawn whether it is open or closed.

Bb5 seems weird without a black knight at c6. Bb5 can create weakness only if there's knight at c6 to exchange, for example after 1. e4 c5 2. Nf3 Nc6 3. Bb5 !? (Rossolimo variation) Bb5 after 2... e6 is pointless and just loses a tempo after 3... a6 which is all the way Sicilian move, where black normally play on the queen side.

I would prefer to see Be2 here. follow that with Nc3 and 0-0 and you have a good solid opening to build on

The move is more common if it terminates in 'check'. That is to say, after Black has played 2...d6. Here, I think it misplaced as Black can, with a gain of tempo, make big - and much-desired - strides on the Q-side.

Well, really c4 is not the best square for bishop with e6 played. After ongoing d5 whites will lose one more tempo. 4. Be2 looks more solid to me here

...a6 is a useful move in the Sicilian (with the idea of queenside expansion via ...b5 later on), so I think the manoeuvre bf1-b5-c4 just loses a tempo. The bishop should be developed to e2 immediately or not at all until it's clear where it belongs.

Back to e2 might have been the better choice, as now 4...b5 would have been a good move for Black. Note that 4.Ba4 would have got the bishop caught in a Noah's Ark trap: 4.Ba4 b5 5.Bb3 c4.

This is a normal move in the Sicilian, this signals the open Sicilian.

Why not 4. ... b5 for black here? Forces the bishop to move again, back to e2, all while expanding the queenside.

Actually it is a good move, and the only idea for black. I mean if there's something black should obviously do - it is to push the d-pawn to d5. I would say that, whites already have no advantage here, but the position is still equal

This is also a developing move because it occupies the centre and lets the light-squared bishop out.

5...b5 was equally playable, in my view.

At last bishop has come to the square he should've come at the first time. Whites has no development advantage, development is rather equal, but blacks better control the center. The only advantage of whites is that they already can castle, but it really doesn't matter here yet. Blacks position is better here, but whites have a draw definitely. All whites problems outcome from 2 unnecessary moves of LS bishop forced by USEFUL moves for black. If i could choose, i would definitely play blacks here.

and a waste of 2 tempi with the B whilst black played developing moves

Blacks took risk to play with an isolated pawn. Personally i don't see reasonable alternatives, but i guess there could be some. Anyway now blacks must play more aggressively, because of potential pawn weakness in the endgame (the general issue with isolated pawn). I don't like to play with isolator, and in this position it doesn't seem like d5 pawn is strong, so evidently whites playing accurately will have a draw at least and even have good chances to win if they happen to transfer the game to endgame. Although blacks have some initiative and d5-pawn is not yet blocked at d5. If they will be allowed to move d5-d4, it will give them reasonable advantage

As Tarrasch said: if you are afraid of an isolated d-pawn, you should give up chess. Understanding isolated d-pawns and hanging pawns is part of ABCs of understanding positional chess.

Why has Black accepted the isolated d-pawn (IQP)? He is looking to attack. The IQP isn't much in itself, though its control of e4 and c4 is very useful. But behind it the field is very open in which to marshal the attacking pieces. The weakness is the pawn itself, and if White were to survive into the ending, it could well become a liability.

10. Nb3 is more reasonable alternative, since 10. Nxc6 doesn't cripple pawn structure at all, but contrarily it strengthens blacks pawn center. Blacks no more have an isolated pawn. I think Nxc6 is a weak move here

I'd have played Nc3 personally...

Nc3 would just lose a piece.

Your knight was right where he belonged in front of the isolated pawn, you should work to get your other knight to support it.

In my view White was right to test this idea. Black is left with an isolated pawn couple, which might become targets for White to attack. However, White will be left with a deal of ground to be made up in terms of mobilization.

There's not much scope for a kingside attack. c4 should be played at some point, probably now.

White's goal should be to blockade the hanging Black d&c pawns, because if they ever get rolling White is in trouble.

The Queen can easily escape the pin, so this is a rather hollow threat. The bishops would look better placed on f3 and f4.

c1 is a pretty good square for the Bishop, White needs to get his prime blockading piece the knight into the game.

How to develop the knight? I think this bishop move is as good as anything White could have played.

Good move and good consideration. d2 point really seems more profitable for knight then c3

Yes, it was good to spot that the Knight is better placed on b3 than the "usual" c3. However, I still think that c4 had to be played.

I'm not that keen on 12.c4, but 12.c3 came into consideration, in order to restrain Black's d-pawn. I probably would have played that, and then N to d2.

not really 4 and 2 pawns. But yeah, two bishops would give any side a good advantage. Although blacks here would never trade their strong DS bishop for a knight. Knight would be better at b3 against isolated pawn at d5, but now Nb3 is rather a weak move.

The d5-pawn is not isolated but part of a hanging dual (although it often becomes isolated). You have a point that control of d4 and c5 is important to keep the hanging pawns restrained.

This induces Black to place the DSB where he really wants it, and white's Knight is left somewhat off-side. I prefer 13.Nf3 with 14.Bd3 to follow. Having said that, though, I'd much rather have the Black pieces in this sort of position.

Bad square for the Bishop, Black's goal should be to play c5 and get his hanging pawns abreast. The bishop blocks the Queen's protection of the d-pawn.

I incline to the view this is a very good square for the bishop, well protected under its pawn shelter.