I like fishing line for aligning fuse pieces - light and strong. At each point where the line passes through the foam, insert a little grommet made of a cut-off piece of a hollow plastic coffee stir stick, to prevent the line from gradually sawing its way through the foam. When everything is aligned, put a dab of hot glue on each grommet to lock everything in place.
I think the CG should start at 25% like a Nutball. And lightness WILL make a big difference to the plane.
Good for you for getting the plane together so fast! I am sure future flights will be much better as you work through the various issues