when sites refer to using a certain volume of concrete, are they referring to pre-mix, or after the water has been added?
The weight of concrete is an approximate theoretical weight. The only way to prove that theory on any given batch is to weigh it after curing.
To the best of my knowledge it includes water weight. The theoretical cured weight of an 80# bag of concrete sack mix including water would be about 85 lbs. OTOH if there is way too much water in the mix, you will loose some to bleed water.
I would go with an 80# and 60# bag of quickcrete. With just enough water to make the mix plastic these two bags will put you right in the target area of 148 lbs per cubic foot. You will loose some concrete to the mixing process, either in the wheelbarrow or mixer.
Another way to do the mix would be with 2qty 80# bags of quickcrete, then weigh the 5 gallon bucket while filling it with concrete.
The best way to add water to mixer or wheelbarrow is with a Dramm "fogg-it" fogg nozzle. The 1 gpm or 1/2 gpm nozzle would be ideal. Not only will the water be introduced at a controlled rate, but the fogg/mist will hit all exposed cement particles at once rather than sloshing some water into one spot.