These all look really good, but I do have a few small suggestions regarding N1 (the early North American units), which looks like a more generic Eastern Woodland warrior from virtually any period of time. A better approach, I believe, would be to draw more inspiration from Mississippian warriors as they were depicted in their own art. Here are some examples that I believe may best highlight some features worth amphasizing:
This image shows a fairly typical Mississippian warrior based on a shell gorget unearthed at (IIRC) Spiro Mounds. In this picture, you can see both the Mississippians' distinctive leaf-shaped loin cloth (which, as you'll see in later images, was worn over or alongside a more typical squared loincloth, possibly to protect the warrior's most valuable jewels) as well as a stone mace and a (likely) hammered copper hairpin and ear gauges. Also note the complex hairstyle, incorporating a short mohawk and beads, and the facepaint reminiscent of a falcon's eye markings (possibly associated with the "thunderers" or "thunderbirds," who were powerful spirits(?) associated with the heavens or "overworld"; these were a common motiff in Mississippian [SouthEastern Ceremonial Complex] and contemporary Native American art and folklore). The belt appears to be made from woven fibers, while the beads inlaid within the warrior's loincloth and used in their necklace might be a mix of shell, bone, copper, or carved stone.
These images depict a chunkey player holding a characteristic chunkey stone (a small round stone like the one shown at the bottom of the left image) and a tool that is most likely a chunkey stick, but which
may alternatively be an atlatl (a tool for throwing spears). Chunkey was a popular sport among the Mississippians and some modern Native Americans in which players would roll the chunkey stone across a flat field, and then throw spears or sticks at it. Whoever's spear got the closest, won. Naturally, it doesn't take a tremendous leap of logic to conclude that this game was likely played by warriors to practice their spear-throwing, and as can be seen with the warrior above the chunkey player is using much of the same equipment. Again note the distinctive leaf-shaped loincloth worn over a more regular style of loincloth (seemingly pushed to the side here - either as a result of the player running, to keep it out of the way while he runs, or
perhaps even to allow for identification of the individual; it's possible that these leaf-shaped loincloths may have born specific symbols or pattern's denoting one's own identity, clan, nation, or other affiliation - as well as his face paint, short mohawk, and well-decorated hair. He also, notably, appears to be wearing some sort of shoe, or perhaps (contrary to the artist's interpretation) slippers.
While the first two images might give you a feeling for the more typical attire worn by Mississippian warriors, these images show a more ceremonial garment, which has sometimes been described as the "Falcon Dancer" or "Bird Man." Clad in a sort of ceremonial feathered cloak or shawl, with a feathery tail and hammered-copper beak mask to boot, it is widely believed that this image is meant to depict either one of the legendary "thunderers" described above or a performer dressed as one of those beings. His regalia not entirely dissimilar to that still used by some Native American dancers to this day, such as by
these members of the Ho-Chunk Nation... Also note what appears to be a chunkey stone, hammered copper disk, or shell gorget worn about the neck, alongside something that may be a whole whelk shell, which the Mississippians were known to trade for (simply see the right image for proof of that!). Alternatively, it may also be a stylistic depiction of a small stone mace or other device.
For an even more maximalist depiction, we have the Etowah Bird Man himself, clad in an intricate head-dress and a flowing mantle of feathers, with a ceremonial mace in one hand and the severed head of his foe in another. Though likely inappropriate for a single warrior, this might depict the grand regalia of a chief, or even one of the mythical thunderers themselves.
Finally, the armored Native American warrior depicted in N2 is pretty clearly based on the "Iroquoian armor" set made by Malcolm Powless-Lynes, which while very impressive and dare-I-say
sick AF, is, perhaps, more appropriate for the earliest period of European contact, rather than just before it (as, per Powless-Lynes' thesis, one of the main reasons that the Haudenosaunee and other peoples stopped using this armor was because European firearms rendered it obsolete, as there
was a brief period of overlap between the use of this armor and the arrival of the first European settlers in the northern part of North America, hence why we have records of it). Thus, I believe that your N2 design
may be more appropriate as a tier-3 unit, while the tier-2 unit might take more inspiration from Mississippian armor sets, such as that seen in this carving of a Mississippian warrior who appears to be scalping his enemy, possibly using one of the aforementioned stone maces (I'll note hear that Mississippian stone maces almost certainly were not battlefield weapons, as they were too brittle for combat. However, they may have still been carried by warriors into battle as symbols of authority worn around the neck [as may be seen above] or, in this case, for butchering a fallen foe):
Note the different style of helmet and seeming lack of side armor or a padded layer underneath the armor, which is worn over a simple loincloth and seemingly little else, which makes this quite distinct from the Iroquoian style of armor researched and recreated by Malcolm Powless-Lynes.
Edit: also attached are some references for various surviving stone maces, so that you can get an idea for what they actually looked like.