I’m glad the answer was of help and that it is stimulating more questions, as things like this tend to do!
I would say, it sounds like you live in an area where it would be best to find some space inside to dry. Even then perhaps a dehydrator or oven with the light turned on may be necessary to dry your herbs before they start to mould. If you are using a dehydrator or stove/oven keep it at the lowest heat possible, just enough to dry some of that humidity off. They are dry when they feel dry and a bit crispy or papery, without much ‘squish’ or bend to them.
I would cut the straw yes, this helps it dry a bit faster and helps with storage, as you mention. And the ‘straw’ is mainly the grassy looking part, but you can include the ‘oat seed stem’ if you would like.
With all the oat processing best wishes,