How do you work with them?
Ultimately in any organization I'd want to know if playables work for us. That is are they worth the investment to make and would we do it again? Also bear in mind that budget spent on making and advertising playables is budget not spent on other mediums, particularly video.In this regard I approach it with its own A/B tests as it is important to get a read on the value playables bring.
Do you separate them from other video ads?
Yes, it gets its own adsets. A/B testing is on lead videos and then on playable versions.
Does it matter on the length of a lead video for playable?
Yes it matters. A/B test on length, content etc. For example I've found that short looped videos paired with playables have a tendency to do better than lead in videos that are 20-30s long. This is despite the fact that the longer videos by themselves often outperform the short looped videos. While this may not be true for every game the point is that the results may surprise you.
Ultimately the playable experience is different than a video experience and you must treat it as such.