Without having door and wanting to order some Jigtech latches, i see they have option of 45mm and 57mm backset. Am i therefore best getting doors as 2 will be part glazed before ordering? Are these standard sizes?
Yes they are standard sizes, you need to determine the width of the stiles on the doors you want, otherwise you risk drilling too close to the glass if you opt for the deeper latch, especially if you've got to plane the door to fit as you may have to remove material from the latch stile, making it narrower.
The backset is the distance from face of the latch to centre of spindle hole mind, just in case there may be any doubt over sizes.