Hey No-Apologies, nice projet.

You can get 1mm thick depron foam from flyingfoam.com

Depronusa.com carries 2mm, 3mm, and 6mm thick depron foam.

I don't know how much weight you'll save over bluecore but probably not enough. The lipos will help but you may need to upgrade to brushless as well, or try the twin fan setup.

I started on a bluecore F-117 about a year ago but only had paper airplane foldable plans. I started to draw some better plans up in cad but went on to other projects.

Good luck!