The first batch was 1,800 lbs. The concrete mixer that I borrowed said that it would handle more than 4 bags (240 lbs) at a time, but it seemed really hard on the machine, so we wound up doing two bags at a time (120 lbs) and that was very manageable.
This was quickrete mix, so it did have aggregate already in bags. I left it for a few weeks before removing the forms and stacking them uncovered in the corner of the back yard where they will stay until spring...