I would recommend defensive Gauls build ONLY Phalanx (for defense) in all villages before moving onto any calv troop.
Phalanx are cheaper and more def per crop upkeep and more def per training time.
In terms of having small off for robbers, swords work good for that
i totally agree with PautheGaul ,phalanx in every village ,train some sword and TT(or haeduan) and 1 ram for seige robber hide out at first time,if you get more resources ,train druids and feed all troops.
druids has the fastest speed in the game for reinforce ,and phalanxs are really good deff with less training time and resources ,and balance in Inf Def and Cav Def.
and also another fact in the game is that ,gaul is the most selected ones ,and teuton deff select spear for first ,and Roman deff is really less ,so Cav Def is enough and Inf Def is less .so druids are better than haeduans.