Yes, preferably, but not impossible. I knew of an acquaintance who went in with a bachelors.
Most of these institutes practice contract, though they called it "renewable contract", and I think even MOE teachers practice contract as well.
There is a salary scale for poly staff, but usually they will try to match your last pay.
But what I know is that the work of a lecturer does not stop at teaching, preparing teaching materials and overseeing projects only. You would still have to act as some sort of "form teacher" to your students, as well as to provide counselling if the need arises. Also, you may be involved in some CCAs/special project groups, as what my source above told me.
If at the moment you have a bachelors degree and some years of relevant work experience, you could even try it now.