A tribe
400 base kobolds plus 20 3rd-level sergeant [mostly sorcerers], 2 lieutenants of 5th level, 1 leader of 8th level and 8 dire weasels.
Using portions of the leveled NPC's gear, distribute crossbows, caltrops, oil flasks, Alchemist fire and acid flasks among the ranks of the fodder.
alchemists fire is not cheap, but the prepared flask of oil are. The oil flasks don't even need to be lit since the PC's [or at least their squares] will already be lit.
Also, look into the "swarmfighting" feat. Just the feat hordes of kobolds need.