I can't be sure because I don't do fermented feed, but I think that means half a cup DRY before you ferment it.
I free-feed, but the figure I've seen is 1/4 pound a day -- weight being more accurate than volume measuring. Again, that's DRY before it's fermented.
Welcome to BYC.
The usual guideline is to limit treats to less than 10% of their diet. That's usually just a tablespoon or so. :)
Where, in general, are you?
If you are in a severe winter area, this article includes tips on feeding chickens that are subject to severe cold...