Is the purpose of the encounter to fight and beat the horde? If so, I'd recommend adapting the minion rules from SotC to Dresden. If the horde is there to harry the PCs, or to make some other conflict (grabbing an item, stopping a ritual, etc.) more interesting you could go with an entirely different mechanism.
An example of an alternate mechanism would be to treat it like a race, where the horde needs a certain number of successes to overwhelm the party and inflict whatever "taken out" result would be appropriate. The horde would "attack" at a certain value (probably at least Epic assuming the PCs act at Superb) and accumulate successes each turn. The PCs would have to split their actions between accomplishing their main goal and beating back the horde. For extra fun PCs could voluntarily accept consequences to reduce the horde's net successes.
The mechanics seem odd, and they are, but if you narrate it right it could definitely simulate a group of people beset by many, many opponents who are dangerous in numbers, but not individually that threatening.