Hello, how can I make the instrument names appear in the first flow only?
Unfortunately there’s no good way to do this at the moment. As a workaround for the time being you could create duplicate players for flows after the first and set their instrument names to be empty (using the Edit Names dialog accessible from the Players panel in Setup mode) but this is obviously a pretty hacky way of achieving it.
Thanks Daniel, brilliant workaround 
Just to add on this topic:
What is the best way to notate a standard (let us say) String Quartet with 4 movements?
a) I notate all movements in one flow. Disadvantage: I will have cautionary key and time signatures at the end of movements 1-3.
b) I notate in 4 flows. Disadvantage: I will have full (or none) intrument names at the beginnig of each flow, so at the beginnig of movements 2-4.
Both solutions give results, that look somehow non professional.
Or is there a third way, exept the complicated workaround mentioned further up?
No, there’s no third way at present. We will need to add some more options for this.