It might be useful to take some spare material and make a mock-up of one down chamber and stuff it with down to get a feel for the relationship between baffle height, baffle spacing, and loft.

I've never used the karo step style of baffle. It doesn't seem any easier to me than horizontal box baffles, which is the most common method.

A common formula to determine the required loft for a given temperature is:

Temp Rating = 70-(20 x loft in inches)

So 1.5" of loft gives you a rating of 40 degrees(70-(20x1.5")).
But if you have 1.5" baffles, the loft will be greater, since the chamber will bulge outward (assuming you use enough down.)

There are lots of variables, though, so it's just a rough guide, and intended for sleeping bags...quilts may not be as warm for a given loft.