Hello Gary,
I buy direct from from Aircraft Spruce & Specialty, when I order, I always purchase two or three sheet at a time because the shipping is almost the same for one to three sheets. 3/32" thick basswood plywood will be much stronger than 1/8" light ply and almost the same weight as the 1/8 light ply. When I am using the basswood plywood for the fuse sides, I do not place plywood doublers, as you would see in many kits, I run 3/8" X 3/8" medium density balsa longerons, the same for diagonals and fuse bulkhead formers. Cores, first I cut the cores then I make lightening hole templates for both sides of the core from the cheapest paneling I can find at Lowe's or Home Depot, next I screw them to the sides of the core with course thread drywall screws ( just a few will do), I then us a soldering iron and make holes in the core in each area of the of template, after that I just take my time and cut out each area with a hot wire. This is actually very easy to do, it just takes a little time. The slot over the tube I cut with a router and a strait edge screwed to the core, and yes that is a carbon tube I place in my core as wing tube extenders both on top and bottom of the cores, at the point the wing tube stops the carbon tube extenders are placed extending toward the tip to around 65% of the wing panel and back towards the root around 20%. Now for the wing skins, I use medium density 1/16 balsa 3" X 48" sheets, I true the edges and tape them together, next I cut 3/4 oz. fiberglass cloth strips 1" wide and place them on the opposite side of the tape directly centered over the seems and utilizing EZ POXY 10 epoxy laminate system purchased again from Aircraft Spruce & Specialty I laminate 2 plies and allow to cure. After cure I lightly scuff over the laminated areas with 320 grit abrasive and clean all the dust away. Using the same epoxy system I sparingly roll the epoxy onto the cores and skins place in the shucks, and into a vacuum bag not exceeding 5 hg throughout the cure cycle (overnight). The nice things about this epoxy system are you have plenty of time to perform your layups with out fear of it going into thermal runaway, it has a low viscosity. I hope this helps. By the way, I glue everything wood together on my fuselages with thin and medium CA only but that is another story.
Bob