Oh, thanks for bringing me down. I feel compelled to give your stuff better ratings now, don't I?
Anyways, layering the details is a good idea, although sheet styrene may be more effective in the long run. Also, be sure to give some elbow room for detail adjustments, instead of filling in all available space with cardboard. However, you're already putting it together in smaller pieces, so adding indented details won't be nearly as hard.
Also a good idea would be to resin it before putting on the final outer layer, so that there isn't as much cardboard/styrene that can shift around without solid support. Not only will this provide an internal support to the finished product, but it will also let you use far less cardboard during construction.