1/2 inch hardware cloth is the wire the vast majority of us use. That will keep most everything up to a bear out if fastened properly and buried or bent at the bottom and run out 18" to 24" to protect from digging. We went outward for under the coop, then covered it with pavers and 1' of large rocks. It helps to have farmers leave piles of rocks near the road for the taking.
Chicken wire is good for putting around your garden or bushes you don't want the chickens to get into but is worthless to keep varments out.
For size of run, 10 sq feet per bird is recommended. Coop is avg 4 sq feet per bird. Most of us will tell you to go bigger.