[bread_baker]

Is anyone going to give these students placement tests? You really need to know the levels that you will be dealing with.
I have taught multi-level conversation classes to adults, but I always knew beforehand what levels would be in each class. I'll need more information before I can give you much advice.
For the first class meeting I would definitely prepare a written needs assessment (a form that the students will fill out anonymously). Keep the wording of the questions very simple and do not use any past tense or high grammar. After the students settle in, you can pair up the highest and lowest students and let them work on the needs assessment together (but still 1 paper per student).
Icebreakers are great for the first class, but the tricky part will be to choose icebreakers that work with a multi-level class.
When will your class begin? Can anyone at the school give you more information before then? You really need to know, among other things, if the class will be a vocational ESL class.