Myrthos is doing all the work here, but still:

When I start a fight or a fight is going to start soon, can I stop/interrupt that fight ? So short: can I run back (flight) when in combat ?

You will be able to (try and) flee from combat, but most of the time, combat will be placed so that you can check enemy levels, or at least their appearance, before you engage. If you are ambushed, it will be in the middle of a zone of a certain level where we know that you have already succeeded in defeating that particular level of creature.

If I understand ONLY the COMBAT is Turn based, correct? So all other actions (walk & talk, travel & trade) are in Real Time ?

Yes.

Is it possible to talk you out of problems instead of fighting ? And if so, give that option also XP points ?

It is possible if it makes sense, and will give XP.

Is it possible to Sneak and pass an enemy unseen ?

Not in our current build, but it will be.

How do it works meeting an enemy ? Do the player take the first action or the enemy the first ? And has this influences/consequences for the outcome of a battle ?

If the enemy spots when you enter their "threat" zone, they start combat. They get higher initiative base scores for the first round. You can spot most enemies from beyond their threat zone, and initiate combat, which gives your party members higher initiative first round.

Can I talk to (any kind of) enemy and say I don't want to hurt him/her and so we go in peace ?

There are creatures that are hostile towards you and are out to kill you. There is no reasoning with them.
There are creatures that are out to kill you, but they are not stupid: if you are too dangerous for them, they will (try to) flee.
There are creatures that are out to kill you, but they are very stupid: you can talk them into NOT attacking you.
There are creatures that are more neutral and only become hostile when you do something wrong, and they offer a way out "the first time".