The DIN connector is generally attached to the monitor, and these are often fairly inexpensive. You can also run high resolution (640x400 monochrome) on most VGA monitors with an adapter. (See http://bales.free.fr/atari/files/text/st2vga.txt for pinout information). Color modes require the ability to sync down to 15.5 Khz, a task that is generally not possible with VGA monitors.
The computer's manual really isn't that useful. If the floppy drive and power supply are internal, it's pretty much a matter of plug and play.
RE: Atari 1040ST monitor 
