Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Strength
ID_BRUSH_BASE_TOOL_STRENGTH
Parameter: Projection
ID_BRUSH_BASE_TOOL_PROJECTION
Parameter: Visible Only
ID_BRUSH_BASE_TOOL_VISIBLE_ONLY
Parameter: Selected Only
ID_BRUSH_BASE_TOOL_SELECTED
Parameter: Size
ID_BRUSH_BASE_TOOL_RADIUS
Parameter: Step
ID_BRUSH_BASE_TOOL_STEP
Parameter: Falloff
ID_BRUSH_BASE_TOOL_FALLOFF
Parameter: Width
ID_BRUSH_BASE_TOOL_WIDTH
Parameter: Hardness
ID_BRUSH_BASE_TOOL_HARDNESS
Parameter: Curve
ID_BRUSH_BASE_TOOL_FALLOFF_CURVE
Parameter: Pressure
ID_BRUSH_BASE_TOOL_PEN