I also agree with conolialfan, that keeping the simmetry in the number of southern and northern natives is not that realistic
North America is significantly bigger (both territory and easily inhabitable areas), and has way more different styled regions
AFAIK you guys currently have:
Apache, Sioux, Cherokee, Iroquois, Inuits, Hurons, Aztec, Maya, Zapotec, Arawak, Tupi, Inca, Tehuelche/Mapuche, Shuar/Jivaro, Guarani
With the addition of
Navajo, Comanche, Algonquin, Carib it would get as complete as it could be IMO:
North: Apache, Sioux, Cherokee, Iroquois, Hurons, Navajo, Comanche, Inuit, Algonquin
Central: Aztec, Maya, Zapotec
Caribbean: Arawak, Carib
South: Inca, Tupi, Mapuche, Jivaro, Guarani
I'm against having lesser known central or southern american tribes just for the sake of having more, or for completing the simmetry between north and south native numbers...
EDIT: Instead of the Algonquin an even better idea might be the Cree. The area is more or less the same, and it can also be implemented as a loose federation. The same way the Algonquin would be or the same way the Iroquois are...
Or if you already have the base work done for the Algonquins, maybe adding both is not a bad idea either
EDIT2: The Comanche is definitely worth including. They had the biggest horse and mounted culture among the north american natives
But while I am not exactly a fan of either the Comanche or Sioux, the Comanche are still fairly well known. (In Texas, Oklahoma, etc. The Texas Ranger arose due to the Comanche etc.) Its just that the Comanche were a more interesting civ. As seen by their map their raids went all the way from Mexico to the Eastern U.S. At their peak there were more than 2,000,000 horses in Comancheria and developed as the biggest horse based civ in North America.
Here is a map of Comanche control and extent of raids in their empire/nation.
http://oieahc.wm.edu/wmq/Apr10/hamalainen.html