Putting a window into an veneer door
 

I would be interested in any advice you have on putting a window into
an internal door to bring light into a dark hallway.
The door is a 44mm flush veneer(1/2Hr FC)
The things I'm concerned about are...
How big can I make the opening without introducing too much flex in
the door? Its a pretty heavy door (50Kg approx) so I's guess this is
solid mdf?
I'm considering a long narrow window (about 6 inches wide) up the
centre of the door. Should I move this closer to the handle side of
the door?
Thinking of finishing this in Stainless steel or aluminium. Could I
take it that an appropriate engineering works would be able to knock a
frame out for a reasonable cost? (approx £50)

TIA
Sean