Only now I found the time for a shoot end of August. Models were all new but was a lot of fun to work with.
As for the technical details: meanwhile I know I have a focusing issue with either my camera or my lens, probably both. As I was expecting it, I used 3 strobes + head flash, all on medium power. That provided enough light to set f6.4 or even f8. Especially the f8 pictures came out perfectly sharp and still with enough depth of field. Till now I was usually shooting at f3.2..4 - not a good choice with faulty equipment.
Two problems when setting the strobes higher: long recharge times and hard to over light the windows. High ISO would help against both problems, but I don't like that (for studio conditions I always use ISO125). Instead I shot at 1/60 and 1/80 speeds, enough for static pictures and solved my second problem.