CWB rule
No artillery, no elephants
Max: 8 cavalry
max 8 foot archers/slingers
max 6 same unit
max 2 horse archers or chariot archers
max 2 german berserkers
(Usualy cwb rule is played at normal unit scale.)

31k rule
No art, No ele
max 6 cav
max2 ha(horse archer)
max3 german berserkers
Attention: sometimes extra rule is added
For example, max4 archers for avoiding overskirmishful battle.
max8cav for eastern facitons
and max 2ele for parthia and numidia etc..
(Usualy 31k rule is played at large unit scale.)

TWPL (Total War Premier League)
No art no ele
Max: 6 cavalry
max 6 foot archers/slingers
max 6 same unit
max 2 horse archers
max 2 berserker
Horse archers count as cavalry and archers