The Singer 347 takes standard 15x1 or Singer 20-20 needles. Nothing exotic about them.
I use size 14 more than any other size and 90% of my sewing is with Coats & Clarks quilting thread which is equivalent to the old size 50 thread. Some times I'll go up to a size 16 needle if I'm doing heave or really thick stuff.
Thanks for the info on the project material.
Joe