My usual take on cage size is that the cage really can't be too big for the rabbit. If you need to catch the rabbit, and you can't because he can elude you, the cage may be too big for you, but for the rabbit, it's fine.
A couple of thoughts on your run . . . . One is that foxes aren't the only things that can chew through chicken wire - rabbits can do it, too. It also rusts pretty fast when in contact with the ground, so it really won't provide a barrier for long. Other wire may be more expensive, but it'll last a great deal longer and be much more secure.
Another concern is parasites. Rabbits in cages seldom get worms, but rabbits on the ground are exposed to the worms and other parasites of the wild rabbits, and can get them. There is also a very large fly called a Warble Fly that is known to lay eggs on rabbits that live on the ground. Warble larvae can get very large; they live just under the skin. It's a bit unusual to see warbles on pet rabbits, but as far as I know, they are never seen on those that are caged well above ground level. You will need to be particularly watchful and regular with your de-worming schedule with a rabbit on the ground.