Why does the simulation not start right away when I press Bake?
When you start baking a simulation, Dynamo goes through a precalculation step before it can start processing. Although this step can take quite a bit of time, especially in heavy scenes, it is necessary in order to make the actual simulation as fast as possible.
How do I disable the floor?
By default, the ground collider is enabled. It can be disabled in the DynamoSolver object by uncheking the "Ground collider" checkbox.