Of the 4, only the Hera marker would create visible lines, so Hera marker it is. I have forgotten how the lines are to be removed. Water? Steam? Need to be washed?
I am also working my way through stitching ideas Goldilock style. Silver machine embroidery thread (top left)? Too thin. Mouline floss (top right)? Too thick. The blue-greyish thread that I use all the time (bottom left)? Perfect.
The random seed stitching plan is out though. I had forgotten how much work it is to get those stitches looking truly random-ish, so I'll be going for a more repetitive pattern.