Another thing to consider about sheep and woodland is that plants such as gorse, bramble and blackthorn can entrap sheep by the wool. When I used to walk my dog in 20 acres of adjacent woodland similar to that pictured, I used to take secateurs with me. The dog would find at least one trapped sheep most days, often more than one. The record in one walk was seven sheep. All were unable to free themselves and would have died, of flystrike, starvation, and or being pecked to death by birds, had I not found and freed them. You would need to be sure you found all your sheep every single day, and be prepared to spend many hours scouring the woodland to find the ones which have become trapped if any are missing on the morning headcount. (A good dog will help to find them, of course - but 100 acres is quite an expanse to search when one is missing!)
Moving electric fence paddocks around is feasible on the face of it, but would become extremely laborious and tedious very quickly, as the areas fenced would be small so need moving every day or two, or if larger, there would be an enormous amount of moving stuff around to do. You can’t in reality leave electric fencing in place, as they get overgrown by undergrowth and or destroyed by livestock and wildlife. (Ask me how I know; we use pockets of woodland and hedgerow edge ground here, electric fenced, and it’s a lot of work each time we go back to one to get the fence operational again.)
And I share the concern about how wet the ground would be outside the spring and early summer growing season, especially once you have cloven feet tromping about on it. You’d need to be sure there were clean dry places for them to lie up all year round, or have winter housing you can take them to.