I got hooked on this stuff with volunteer bloodgood seedlings.
Buy a sleeve (or a case) of 5" (daffodil) paper-white pans, and mix up a barrel of soil and pot up 25 or fifty. (or 500)
No, no potting or pro-mix. Build your own soil out of pine bark mulch and granite-grit from the Blue Seal, or Ralston Purina store. Soil made of peat moss, coir, or loess will just kill seedling Japan maples. Trust me, I killed a few hundred till I switched over.
The sugars maple trees make and organic fertilizers make an irresistable combination to mice vole and chipmunks. Use only Osmocoat or soluble fertilizers only. Disregard this and those four legged vermin will chew every seedling to a stump. You was warned.
If you have enough other stuff to keep you busy and 15 or 20 years to fritter away, blood good and other open pollinated landscape Japan maple make very suitable starter trees.
As you continue with this, keep an eye out for Hime examples. You will have to propagate them as they do not have reliably fertile seed. What Hime has got, is a fundamentally smaller leaf and shorter internode length. It just plain makes a more credible small tree.