I have them growing natively on my farm in VA. They are not that large. 12' should be plenty of room for them. They are susceptible to blight just like American Chestnut. The difference is that the blight does not seem to keep them from producing nuts. They seem to die back and then resprout from the roots and continue producing nuts. Most of mine seem to be more in this bush form because of the blight dieback but they still produce nuts. I have a few that are full tree form. If you think yours will get to full tree form, you may want to space a bit wider but you don't need too much.
Thanks,
jack