Ok, I have stacked a few questions
To many questions and too few tutorials probably I could figure most of them myself but I am impatient ...
How exactly do satchel objectives work? I make my destroyable mesh and place a satchel objective actor and simply combine them through tags?
I want to make two different satchel objectives which have each three destroyable meshes both of them are active at the same time.
After the meshes are destroyed I want to activate a capzone.
I didn't find the SDK manual too helpful and there are basically no other tutorials specfic to RO.
To do this you just need a ROObjSatchel actor instead of a regular ROObjective actor. You will also need a RODemolitionVolume (check the doors on StalingradKessel) to give a location for satchels to detonate within and trigger the objective.
For the 'two satchel objectives with three destroyable meshes each' problem you may have to dive into an AIScript that waits for each mesh to call an event upon destruction before triggering the objective itself. I'd have to set this up myself (might be able to tomorrow if you're around and I have time) because I can't really picture how everything will work right now without actually experimenting a bit.
Is it possible to activate a mover after a objective is completed? (--> door opens after satchel objectives are blown up). I mean it is possible, but with out writing new code?
Yes, you can do this without new code. ROObjTerritory Properties > ROObjective > AlliesEvent/AxisEvent. Put an event in here and it will get called when the objective is captured.
And also how do I make breaking glass sound like breaking glass? I got the glass breaking when I fire at it and the correct emitter is showing but I don't see where I tell the actor to play the sound if it breaks.
As DH mentioned, take a look at Krasnyi and locate the ScriptedTrigger that is nearby. Check out the ScriptedTrigger Properties > AIScript and you should see WaitForEvent/PlaySound/GoToAction.
Next question

Movers and sound: I sucessfully created a mover (aka a door) but the mover sounds I set play always, constantly. They play if I open the door but they even play when I am a mile away. Where did I miss to set my cross?
Have a look for a door in Odessa or Krasnyi to see how they work. Select a door, hit F4 (to get into the properties) then go to Mover Sounds > OpeningSound/ClosingSound.
Another problem I have is my preview screenshot in the mapselection is not shown. I didn't make it a material or screenshot seqeunce just a simple screenshot. I sucessfully imported it into myLevel, compressed it and told it to appear in Level Summary in the Level Properties. I had less problems with importing my overhead screeenshot ...
Can't think of a reason for it not working at the moment... I can Kettch you on IRC tomorrow.
Btw, did you see what I did there? I has clevers. 
That should be all ... for now