1) If there is a enemy in the staging area and I dont have enemies engaged, can I Sneak Attack + Son of Anor after the stage where enemy attacks, engage that enemy and then attack with Son of Anor and other characters? Doing this, I can attack without being attacked.

2) The text "Player cannot advance while X is in play." mean that I cant go to the next quest or that I cant put progress token in the quest?

1) Yeah sounds legal, no problem. The phases of the combat round proceed whether or not there are enemies.

2) You can place progress tokens, but cannot flip the current quest card.

1) Yes, provided you are referring to an enemy that has higher threat than yours (and hence remains in the staging area during the encounter phase).

2) Generally speaking, it means that even if you have enough progress tokens on the quest stage you won't advance while X is still in play. Case in point: Journey down the Anduin. As long as a Hill troll is in play, you cannot advance to 2A no matter how many progress tokens you have on 1B.

Thanks people!

I have one more question:

3) If I use Quick Strike to attack a guy that I'm engaged, can other characters help the guy that quick striked?

no. Make sure you QS after the shadow card is revealed, that is the best time. Often you do not need as you know if you want to attack, but it is a good habit to get into as it basically becomes a shadow effect protecting card as well.

It is a good and awesome tip, I will remember it! Is there somewhere where I can find a list of tips like that?

But also, if I do that, i would need to exhaust someone for the defense. I also need to remember that.

no. Make sure you QS after the shadow card is revealed, that is the best time. Often you do not need as you know if you want to attack, but it is a good habit to get into as it basically becomes a shadow effect protecting card as well.

Well, carefull with this. Most shadow cards boost attack, but some shadow effect are "raise your threat by 8" and Quick Strike cannot prevent it.