Ok, don't cook the starch. Keep it as cool as possible. You want the starch to be incorporated as fine granules IIRC. That causes the matting effect to be best. All you need do is swell them.

If the emulsion comes of in sheets or ribbons, or if it forms blisters it is hard with poor adhesion to the paper. If the emulsion dissolves, then the emulsion itself is not hard.

The gelatin, as you coat it, should be no higher than 10% and should not go down at more than about 750 mg/square foot. If you get more or less, you have problems. The hardener, at 10% (chrome alum) should be 10 ml / 100 ml of this solution and should harden in about 1 day.