Titleblock and Plot Background

OK. Another crazy cad issue to tackle.

Can someone please tell me if my 24 (high) by 36 (wide) TITLEBLOCK should
have its lower left hand corner at 0,0 AND whether when I xref this into a
PLOT SHEET in Paperspace I should insert it at 0,0? Can someone also please
explain to me what the white background on my plot sheet is and how I set
whether it shows up. Can someone explain the black dotted line and why it
appears to indicate the extents of the printable area, but when I get an
actual print it is usually wildly off of both the white background area (and
the dotted line) and why it is also apparently off of the Print Preview that
I run that seems correct?

Brand spanking new HP Inkjet Printer so no offset issues with the printer on
anything else.

I always seem to screw around with the PLOT OFFSET option a million times to
get this to straighten out but there must be a better way...

Thanks in advance,

Jonathan

P.S. I actually plot onto 12 X 18 inch sheets by scaling the Plot 1:2 which
gives me a half size set (and keeps me from having to redo all my plots or
having to do two page setups when I got to get them out 24 X 36) if that
matters...

 

Plot Extents.