At least four layers, maybe 6.
One layer for the 3 mm 12″ circle.
One layer for the 3 mm mosaic piece (unless this is a 3 mm piece w/3 mm mosaic pieces tack fused… I don’t quite understand from your description. If so, then it’s 2 layers).
Add those up and then multiply by 2 because it’s a tack fuse.
Fused Glass Designs
dba Jester’s Baubles