Maybe you could treat them as a swarm (A swarm is technically 300 Tiny creatures).
You can only control one andead at a time, how does this work with Command Undead in Pathfinder? It strike me that you wouldn't be able to command the andead as normal undeaad and perhaps you you'd have to command each one separately. That would take a lot of rounds to do. I recommend that since each andead is 1/8th of a HD, you could command 8 per HD.
In 3.5: "T"he cleric must take a standard action to give mental orders to a commanded undead. At any one time, the cleric may command any number of undead whose total Hit Dice do not exceed his level."
At 5th level, the most andead that you can command is 40. Theoretically, you'd have to be 8th level before you could command 300 of them.
Debby