Karin that sounds like a totally reasonable place to start. And yes it is 4 calories/g for both protein and carb and 9/g for fat.
I wonder if you did a couple of days (or a week) where you kept to the 1700 calories and the 20g or so carbs but let the fat and protein fall where they will and see where you land naturally and if that would give you a downward trend on the scale? Then you would have some data points, and if you lost week on top of that you would know you don't have to be so hard nosed about the macros.
Hope I am not confusing the issue here.