scilian defence dragon variation

First , this is not Dragon. 

You can have dragon variation only in open Sicilian and in no other case. So if white doesn't play 2.Nf3 and 3.d4 , it's not dragon. 

1.e4 c5 2.Bc4 with 3.d3 following is Bowdler attack in Sicilian either you fiancheto your bishop or not.

In your example 4...g6 is innacurate because after the exchange 5.Bxf6 exf6 , Black has a bad weakness on d5 with rather minimal compensation(the pair of bishops in a position that is semi closed is not such an asset).

Nothing decisive yet but Black's inaccurate play has justified White's slightly doubtful second move.Most would be very happy to play this with the white pieces.

     Once white plays 2.Bc4 it is much more reasonable to play 2...e6 to blunt the bishop(and of course forget Dragon).Not that 2...d6 is a mistake but trying to play the same series of moves against everything white does is certainly wrong. Learn to adapt to your opponent's moves.

Well , many questions. I will try to answer and if I forget something ask again.

      It is bad to start a game with the plan to fiancheto the bishop and repeat the same moves without taking into consideration your opponent's moves. This is wrong chess and it will eventually fail plus it's a very bad habit that will hurt your improvement. It's never good when you are not thinking and you rely on predetermined moves.

     The bad bishop on c8 after e6 is a "problem" but it is a minor one. Unfortunately in chess you can't have everything. Sometimes you have to give something to take something back. In this case Black temporarily sacrifices the activity of Bc8 but he gets some interesting options against Bc4 as compensation.

Here is an example:

Now the weakness on d5 is not a decisive one but again everything in chess has to do with what you give and what you get in return. Black in this case weakens d5 and he doesn't get much. In other cases though , it might be acceptable if he gets more. It's a matter of evaluating the cons and the pros and deciding.