4.
Races :
Cromagnon (Humans), Neanderthal (Half-Orc stats), Austopithecus (Apemen -Halfling stats?), Lizardmen, Gnomes (because I like them

)
5.
Classes
Fighter classes'
Hunter (modified Warrior with Track and sneak attack)
thanks to Gez
Cannibal Savage (Barbarian)
Rogue (Scout)
Warrior (rare fighter types)
'Magical Classes'
Shaman (Druid)
Bard (Storyteller)
Scorcerer
Ranger (greatly modified but sombody had to guide their nomadic wanderings*maybe a PrC)
Expert (modified to PC status eg Skill focus feat, masterwork ability etc)
Prestige Classes
Spirit Champion
think Paladin: The Champion is the chosen vehicle of a Beast spirit (Shark, Crocodile, Boar, Giant Eagle, Tanifa Dinosaur, Smilodon etc -often the clan war god) who imbues their Champion with a part of their power
Wizard:
think Cave Paintings as gigantic non-portable Wizard Tomes in which the Wizard must meditate each night in order to learn spells
Priest (non-combat):
As society become more settled it starts to develop gods (as opposed to Spirits) and the Clergy emerge
6.
Plot seeds
My current homebrew is set in Mythic Polynesia and its peoples are neolithic mariners.
IMC the PCs are the 'champions' of their community which is a group of settlers newly arrived on a new island.
The campaign started with the PCs being sent from their homeland (which was sinking into the waves - something that has happened irl Polynesia) to discover a new land.
They found Paumako a large island whose native inhabitants include clans of gnomes, a family of ogres, clans of goblins and a Sahuagin lair a short distance off the coast.
First Adventure -
Explore Island, meet gnomes (and avoid tresspassing on their burial ground), explore (ogre dominated)mountains and recover the 'Heart of the Land' (an artifact) from the Spider Caves (thanks WOTC)
Second Adventure -
Establish a settlement - Fetch settlers, build village, harvest food, use diplomacy to keep everyone happy
Third Adventure -
Villagers have tresspassed on gnome burial ground!, the gnomes are going to sacrifice them to the Feindish dire eel that inhabits the Sacred Pool. - Save Villagers, restore relations with Gnomes, respect Eel god
Other adventure hooks could include fighting off enemy raids, killing the monster which is attacking hunters, making a raid on a neighbouring village to steal women
PS
Slavery
The practice of Wife-kidnapping is NOT slavery. It was practiced in my culture (as recently as the 1940s) and the captured wives were thereafter well treated members of society. Remember there was something of a cultural expectation that wife capture might occur and so low status people were socialised into accepting it. Of course when it happened to a chiefs daughter - that was a whole different story!!!