Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Strength
ID_BRUSH_BASE_TOOL_STRENGTHParameter: Projection
ID_BRUSH_BASE_TOOL_PROJECTIONParameter: Visible Only
ID_BRUSH_BASE_TOOL_VISIBLE_ONLYParameter: Selected Only
ID_BRUSH_BASE_TOOL_SELECTEDParameter: Size
ID_BRUSH_BASE_TOOL_RADIUSParameter: Step
ID_BRUSH_BASE_TOOL_STEPParameter: Falloff
ID_BRUSH_BASE_TOOL_FALLOFFParameter: Width
ID_BRUSH_BASE_TOOL_WIDTHParameter: Hardness
ID_BRUSH_BASE_TOOL_HARDNESSParameter: Curve
ID_BRUSH_BASE_TOOL_FALLOFF_CURVEParameter: Pressure
ID_BRUSH_BASE_TOOL_PEN