It might be better having Uden in the advance party - Garak fights from inixback, and you'd need two invisibilities to cover him and his mount. With a 50ft move, Garak is just as good a rapid-moving reinforcement as Uden, and he hits harder when he is charging anyway.
Divine casters are pretty light on concealment magic. What Garak can do well is sow confusion. The combination of an Insect Plague and the effect of his Fearsome armour should mean we can make sure we don't face the whole organised enemy at once. With summoned creatures and Giant Vermin, we can probably make sure we outnumber them when we do choose to fight.
If this is only a small patrol, however, I'd prefer not to use the higher level spells, considering there's 700 gith out there somewhere still to be dealt with.