Great to here!! Get those posts in virgin ground. No fill.
A couple other thought starters.
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Are you doing radiant heat? Even if no, put the pex in for later - google blueridgecompany dot com and look up their pex and manifold pole barn package. You want the RHT Pole Heating package with Pex B tubing and manifold. The RHT-PB-1800-B-1/2 kit is $720. You can't hardly add it later. Once you buy it tell Blue Ridge to send you a pex layout plan - tell them on what wall and where you want the manifold. You want those six loops to be as close to equal length as you can make them and have as close to 9" spacing as you can have.
What about 2" extruded polystrene high density foam under the pad? Start looking for foam deals on craigslist now. You need 50 sheets. From the borg it gets pricey quick.
Tyvek tape - buy a 6 pack of rolls off ebay - cheapest place I have found it.
I also like Mesh-Ups concrete mesh support chairs. Google them. 1/2" pex is 5/8" OD. I bought 2" mesh ups. that left me plenty of room in my 5" concrete to do a 1.5" expansion cut. These things are sweet and ensure you pex is in the middle of teh slab and they do not break and crush when walked on. You want them every two feet. After I had my concrete guy order them he sells them routinely now. He had never used them before my pour.
Also if you have ever had the desire to pull against your concrete - like for a car or pulling something heavy off a trailer - check out the Champ Anchor Pull Pots at autobodytoolmart dot com. Also get the Instant floor plate for them for new floor install. Again something much easier to install in a new floor especially one with pex in it.
Id suggest a few pieces of conduit and PVC through the floor as well for things like electrical, any drains, water lines, etc.
Glad its my shop I am responsible for - I only have to make me happy.