True.
No, MSD also has a requirement for specialties, five for PADI.
No, Divemaster is the first professional level. MSD is the last recreational level, and is not required for divemaster.
MSD, at least for SSI, requires that. AOWD requires 4 specialities with CheckOut.
DiveMaster is the second professional level in SSI. The first one is Dive Guide. Dive Guide + Science of Diving = DiveMaster
There is no requirement to start the Dive Guide Professional course to be a MSD. AOWD + Rescue + 60 logged dives is enough. However, those requirements are the same or a little bit greater than for MSD. MSD is a Recognition level. No academic is required, so, to start the Dive Guide course at least you need the same requirements than MSD.