It's a chapter One, the first day when buying a bicycle. No "from the first day" but "the first day". Of course, there will always be a few millimeters here and there to adjust, but should not be more than that after the initial setting.
Saddle height and setback (and "flatness", although, that can be just slightly adjusted in the process) is the first adjustment from which everything else is follow.
Maybe I'm wrong, but somehow I have the impression that you are not sure where to start to get a proper/comfortable body position on the bike.
Handlebar ... This is a slight "old school" profile, so you can get drops parallel to the ground or fine flat transition to the hoods. Cannot be both in this case. You decide what's more important to you, there is no rule for that.
But it would be good that stem length is correct, then it's all easier to set.