Ok, so Turkey supports non-government troops on the territory of neighbour country. Isn't it called international terrorism?

Even if that's true it will be impossible for Russia to use that as an argument since they are actively doing the same in Ukraine.

It won't be an argument. In 2012 Turkish plane was shot down over Syria.
Then Erdogan said that 'speeds of military jets are too high and it can sometimes get into other countrys airspace'.

Now some Turkish jets could fall down again... Or kurds wil get some new nice weapons from an unknown friend... In any case this will get an answer from Russia. And after that... It all goes down on how will NATO behave...

If Russia supplies the Kurds with weapons to attack Turkey then hopefully we'll see a full scale NATO invasion into Syria and Iraq, depending on where these attacks are coming from.

Unless the rebels they supported engaged in terrorism, which I've not heard any aligation of let alone seen evidence for, no.

According to a FSA source the FSA opened fire on one of the pilots as he was descending using his parachute:

FSA source:

The dead pilot shown on video tried to fly his parachute into regime territory. Our fighters "shot him dead from a distance."

— Charles Lister (@Charles_Lister) November 24, 2015

This would be a war crime against a Russian pilot, which will without a doubt lead to an immense reaction from Russia against the FSA

Article 42 outlaws attacks on pilots and aircrews who are parachuting from an aircraft in distress. Once they landed in territory controlled by an adverse party, they must be given an opportunity to surrender before being attacked unless it is apparent that they are engaging in a hostile act or attempting to escape. Airborne troops who are parachuting from an aircraft, whether in distress or not, are not given the protection afforded by this Article and, therefore, may be attacked during their descent.
https://en.wikipedia.org/wiki/Protocol_I

Two weeks or so ago the city of Latakia (which was untouched so far by Syrian war) was hit by missiles from the region the plane was shot down now. Many civilists died - the source are the rebels. The rebels are terrorists, Assad is a murderer, Erdogan and Putin are both dangerous cowboys, Saudi-Arabia is fueling the conflict. In this stuff no one is good or right.

I don't support Turkeys actions as this can escalate the conflict out of syrian borders.

That was believed to be by a diffrent alqaeda linked rebel group. There are many diffrent rebel groups in the country. Some like isis are also terrorists.

Video said to be showing FSA forces destroying a Russian rescue helicopter using a TOW missile. 1:30 is where the helicopter gets destroyed.

FSA has "gunned down" both pilots as they were descending using their parachute:

Abu Ibrahim al-Sheghri, a rebel from 10th coastal brigade in Syria, tells CNN fighters machine gunned Russian pilots as they parachuted

— Ivan Watson (@IvanCNN) November 24, 2015