Is there any POS right now ?
Or does the POW has to be done before stacking begins on the Qt wallet ?
No POS yet, and I haven't seen any clear timelines on when that will be coming. My guess is not until 2019, or best case scenario, later this year.
We have a roadmap that will be followed, on the roadmap we promise PoS in Q3 of this year. We'll do everything we can do get it ready before that but worst case scenario it'll be done in Q3.