*Here* optimal planting dates for wheat is Oct 1-15th.  Optimal planting date for barley is Sept 20th-Oct 5th.  So, you can see that optimal planting date is 1-2 weeks earlier for barley than it is for wheat.  If you plant late, you will take more of a yield hit, compared to planting wheat late. At least, that has been my experience. Hessian Fly-free date is not an issue - at least we don't get concerned about it.

Barley will not handle wet ground as well as wheat will; and barley will winter-kill quicker than wheat. Plant your barley on your well-drained soils.

You can have head scab in barley, just as you do in wheat. Most guys feed barley, so they don't worry about it. However, it can occur. 

Yield of barley will depend on management.  Push the fertility, use a growth regulator, to get top yields.  I've seen 100+ bu/acre where management pushed it. I've seen 60 bushels where management did not push it.  All depends how well you will manage it.