Hi Scott,
What you are describing sounds great... though somewhat expensive up front, compared to moving fences. I would suggest making the fences as temporary as possible to start with, so you can adjust things after you actually get the sheep in there. What you think is a good size or shape might change once they have grazed it a few times. I would also get two chargers if possible. Even if you are only using one at a time, it would be good to have the backup in case one dies.
Here is a video from Joel Salatin talking about a paddock system for pigs. I know you are going for sheep, but some of the principles might apply, and there are some nuggets about electric fencing in there as well.
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