Spoiler alert! I've never built an earth bag wall, so my input might not be worth much. Years ago I did work with others to fill several hundred of sand bags and I assume it would be roughly equivalent.
Taken a bite at a time, over several years I think it could be done, but it would definitely be a long term
project. What would you use to protect the bags from deterioration due to sun? Adobe, lime or cement come to mind. The first two would definitely need some kind of capping protection. That much work
should definitely be protected.
I'm wondering if a cow having a comfortable lean or rubbing an itch against such a wall might shift things unless it was a couple of bags thick.
I applaud your ambition and work ethic. Such a wall, all around a 4 acre plot would be over 1600 ft of wall long, minimum. I've notice most earth bag buildings I've seen on youtube have been modest, about 60 feet or so of wall. Even if the wall were 8 feet tall, that would only be about the equivalent of about 120 feet of your wall.
Generally speaking, I think very long earth walls are best left to powerful sovereigns who can call up massive peasant levies to implement their grand designs. (I personally find other people sweating and heavy labor is so much easier for me to bear than my own, unless it's griping teenagers, then, not so much.)
I think I would be tempted to plant a seaberry or osage orange hedge (or something equivalent for your climate), with, maybe, a four foot wire
fence imbedded in the heart of it, and leave earth bag walls for your zone 1 areas.