Can I connect my HF-500/MM-1000 spindle and 3D printer to the STEPCRAFT at the same time?

Yes you can with the use of the of the STEPCRAFT System Attachment Switch Box.  To use the Switch Box, you simply plug a serial cable from the Switch Box to the serial port on the CNC and then you plug the 3D Printer and the HF500 Spindle into the respective ports on the back of the box.  Then you can just rotate the dial to select the attachment that you would like to use and mount that attachment into the tool holder on the STEPCRAFT.