I'll be flying FlyNiki for the first time in the next two days, ZRH-VIE and VIE-CDG.
Please note sometimes there a AB, 4T aircraft whit AB Catering.
can I use the Air Berlin app to check in?
Yes 100%
From when on can I check in online?
http://app.mobile.airberlin.com/en/webcheckin
One small rollable suitcase ("cabin compliant TUMI") + one computer bag, is that OK?
normally no but the crew ignore that.
AB is part of oneworld, but not sure about FlyNiki.
http://en.wikipedia.org/wiki/Fly_Niki
This is your first time in VIE?