For anyone interested, a similar discussion came up on BGG yesterday (and unsurprisingly ended up in the same "FFG should make a 'player cards only' pack" place):
https://boardgamegeek.com/thread/1754301/4-players-after-dunwich-concludes/page/1
In answer to the original question: I believe with one Core + one of all Dunwich products you will end up with about 130 level 0 player cards, which is enough for four legal characters. I had a go at building decks for a Zoey/Rex/Jenny/Agnes team using the currently available card pool and, while they won't be as powerful or consistent as with two Core Sets, I think they would be fine to play on Easy or Standard.