The problem with Garmin's Edge series is that they cannot 'read' the digital routes that ACA has made available. You need a dedicated GPS (like the mentioned Etrex 20/30 models) for that. The Etex (or like unit) can accept the ACA download and give you those turn by turn directions you're looking for (assuming you've loaded the Navigator/etc maps). Even with a dedicated GPS, it probably can't hold all the waypoints for an entire cross country route, meaning you'd have to download a portion into the unit and somewhere along the trail, find a means of downloading the rest.
My wife and I used our Edge 605 when we did ACA's Adirondack Loop last spring, but we had to take the ACA paper maps and laboriously plot the route into RideWithGPS and then download the created route into the Edge. Difficult enough for a 9 day trip, totally impractical for a transcontinenal ride.