Documents setup at 50% should be at least 260 dpi:

BB 840
At 50% width = 420mm,  height = 1057.5mm

BB 990
At 50% width = 495mm,  height = 1057.5mm

BB 1190
At 50% width = 595mm,  height = 1057.5mm

Don’t forget to add the equivalent of 20mm bleed on all sides at final size. Also in document set-up allow for a non visual margin of 25mm at head and 90mm at foot at final size.

Preferably artwork should be created at final size 1:1 scale.

130 DPI JPEG (preferred).

All colours must be converted to CMYK
For rich black use 80/60/40/100