Thanks for the replies! Anybody else got some more ideas? Games, initiations, ideas for NPCs, etc.?
Background: The tribe is warlike with kind of a druidical/shaman type religion (nature spirits, trinity of gods: war god, his wife, trickster son). They practice extensive blue facial tattooing on all members of both sexes from a young age that outsiders find hideous. They are know for torturing civilized captives so badly that it's better to die than surrender to them. They are regarded as "subhuman savages" by their civilized neighbors and there is a debate as to whether they should even be enslaved they are so ugly and dangerous--they are fit only for the gladiatorial arena. The tribe are semi-nomadic hunter-gatherers with some agricultural skills; they change camps every decade or so. The tribe is patriarchal and patrilineal; females are seen as inferiors but treated well (they aren't warriors). The women of the tribe mock the men unmercifully for failing at anything--a warrior will often stay awy from his tribe for days rather than face their cruel barbs. Since women are seen as inferior, he cannot respond to their insults or he will lose face among the other warriors. Some women are allowed to be shamans but that is the only career path outside of wife and mother.
The chief is trying to forge an alliance of tribes with himself as warlord to sweep down from their northern forest home and conquer the civilized southern kingdom as they did once several hundred years ago.
The southern kingdom's religion philosophy is "might makes right." They desire to exterimate the barbarians completely and sponsor periodic crusades against them (which have all ended badly for the crusading knights). The southern kingdom's god is one of fire, torture, slavery and plague (LE in D&D terms) but the kingdom was once ruled by a brutal theocracy of a god of death, evil, undead, chaos, revenge (CE) who still control the country's largest port and only free-city. They scheme to restore their power to its former levels and beyond (they pay lip service and tithes to the king). These two evil gods dislike each other but have a precarious alliance against the gods of the neighboring kingdoms withg whom political relations are strained, to say the least. The followers of the fire god are totaly into feudalism and evreyone knowing their place in the pecking order while the followers of chaos desire to do away with feudalism and replace it with a "meritocracy" where anyone can rise to any level--so long as they worship the right god--theirs.
The chief of the barbarian tribe we're developing has some kind of prophecy to uniting the tribes--which are fractious and hostile to each other--but the other tribes aren't necessarily going along with him yet. He has (or had) civilized allies (the south is on the verge of civil war with its rebellious northern province--the only land route to it goes right through barbarian territory and the earl of the north has used this to his advantage).
By the way, I found the following site super-helpful:
THE BARBARIANS
And more specifically, this page within it (includes map of a fortified barbarian village):
BARBARIAN DAILY LIFE
Also, this site had a concise article on huts with tons of color photos!
CELTIC HOUSES