I like all your improvements. You clearly take to heart the advice experienced chicken keepers have to offer.
The only thing that concerns me about your drawing is burying the legs of the coop in earth or concrete. They will eventually rot out. I had great pictures of what happened to my fathers front porch posts but can't find them right now. We had to tear out the porch and replace all the posts.
I set my posts on adjustable 1" offset post bases on concrete piers when building anything elevated.
As for your floor, 1/2" plywood is fine. Your 2x6 "beams" do not need to be treated. The sheathing on the sides of the coop will be brought down to cover it. You will build your walls such that the top of the tie plate is 8' from the bottom of the 2x6 so your wall sheathing will cover everything.
Hang your 2x4 floor joists in hangers flush with the tops of the 2x6s. I would go with 16" on center instead of 24" OC though. Just get five 2x4x10' boards to cut for your floor joists. For the two end joists you can use hidden hangers.
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I would also notch the 4x4 posts so the 2x6 beams sit on them instead lag to them. It's much stronger that way... and per the IRC, not that a coop qualifies but why not built it that way?
After I set a beam on top of the post and butted up to the notch, I'll nail into the notch. The notch side needs to face towards the inside of the coop so you can install the joist hangers into the wood without interference from the post to beam connectors, if you use them. These are also sold for anchoring your beam to the post on the opposite side of the notch:
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This way, you will make a perfect 5'x8' area to put your plywood floor on. The 3'x8' piece of plywood you will have left from ripping the second sheet to cover the floor can be used to fabricate your nest boxes or go towards your roof sheathing.