I don't think 1 would suffice and, no, they don't come charged with PG. You may want to investigate making a humidifier with some florist's foam (do a search for directions)...it will do the job and you could be using it almost immediately (not waiting for one to be delivered).
Hope this helps:)
P.S. - don't forget to get a digital hydrometer (NOT ANALOG), as this is a fairly large space and I'd want to monitor it closely.