In an ongoing campaign, I use the following composition for my legions (based on this post: https://forums.totalwar.org/vb/showthread.php?t=101787 ); I'm still the polybian period, and the composition has not changed much from the camillan period:

for a legion (halfstack); so a consular legion is two of these
1 general
1 hastati
1 principes
1 triarii
1 leves
+ alae:
1 allied skirmisher
2 allied infantry
1 allied cavalry
1 elite infantry (pedites/hoplite)

examples of allied skirmisher/infantry/cavalry sets:

Ligurian:
Ligurian cavalry
Ligurian infantry
Celtic Archers

Sicilian:
Hippeis
Syracusan hoplites (modded the EDB to allow recruitment)
Toxotai/peltastai

But I've yet to reach the Marian era, so I don't have the composition for a legion of that era, but you might want to refer to the link I posted above