Desired speed means maximum speed. When there is nothing restricting the entity, it'll travel at its desired speed.
If entity's desired speed is 1.4 and the path maximum speed is 2.0, the entity will travel at 1.4.
If entity's desired speed is 1.4 and the path maximum speed is 1.0, the entity will travel at 1.0.
Initial Desired Speed is a property. Every entity starts at this speed. You can change it mid-run by assigning a new value to the Desired Speed state.
It is a constant speed, unless you code it otherwise somehow.
Yes, unless the entity is restricted by the path maximum speed or slower entities blocking the path.
Use the expression ModelEntity.Movement.Rate.
ModelEntity.DesiredSpeed returns the entity's current maximum speed, not that instant speed.
I tried to compile all my answers in a single model. Check the file attached at my post.