It all depends upon how far apart you are planting your trees. The Acer rubrum 'Autumn Blaze' will grow to 40 ft wide and 50 ft tall. How big are the Japanese Maples? Most (except the dwarf grafted) will grow to 30 ft high and wide. So, to not crowd them, you would have to leave about 50 ft between trees.
If you are going for a more foresty look, you can plant them closer together. I planted an entire grove of Japanese Maples and Eastern Dogwoods with an understory of azaleas and ferns on a north slope in the California foothills. I planted the trees about 6 to 10 ft apart and ended up taking some out as they grew. As I had grown all the maples and dogwoods from seed, the only expense I had tied up with them was time.
