The thread in my samples is C&C cotton, not sure of the ply/wt. Seems to give me the best stitch tension. I used Superior mono-filament on the top and beige C&C in the bobbin. Pic of backing is attached.
The heart is a stencil design that will be on the front of the quilt, mainly in the brown borders and in the 4 corners in the red/pink/white fabric.