Stippling would be just fine for placemats! I always use exactly the same thread in the bobbin as in the needle, so I choose the thread color keeping in mind what it will look like on the reverse side, too. To save time, I think I'd pin many of these onto my leaders (if possible) and quilt them all at the same time. I did some placemats last year which had appliques on them, and I loaded a huge sandwich, quilted it with a pantograph, then cut it apart and put on my appliques by machine, through all layers. They were also bound at the end. Good luck to you!