DEVICE is used to uniquely identify a 'Part' something that you would buy for the board, say a memory. PKG_TYPE defines the decal used in PADS, many DEVICES will use the same decal (PKG_TYPE) so it is more efficient to have many devices using a single PKG_TYPE rather than duplicating the information.
I can't answer for your second question on clearance rules, the question might be better posed on the PADS PC community.
What properties do you think you want to send to the PCB? It is possible to transfer most properties by editing the startup files and configuration of the PCB transfer.
I have passed, Height, Description, Value, and even the Datasheet hyperlink.