I think it is fasle weight economy to save on spokes. I'm conservative and use 32 spokes. A spoke just weighs about 6g, so you save 72g to go to 20 spokes. but have limited rim and hub choices. it is also more difficult to true fewer spokes. and if one spoke breaks out of 20 (which is more likely than 1 out of 32), the wheel is much out of true or even unrideable. a 32-spoke wheel can deal with one broken spoke to get you home, especially if you have rim brakes.

At your weight i'd risk using 28 spokes, but wouldn't use 20. but you may be lucky. those are what they call race day wheels and people use training wheels for normal riding.

Make sure they are equally tensioned, double-butted and have a good rim.