Why did my "Turkish Delight" turn into a horrible goopy mess?
I've worked with agar a lot, and made a few things from the HRC. Of all of the things you've identified as possible problems, I think the biggest likely ones are the quantity of agar, and the agar powder itself. Everything else about the cooling issue is normal. Agar powders do vary. You want to find one that is pure, unadulterated agar, not one that is setup to be a pre-prepared dessert as those are weaker.

If just for a laugh you want to try to save this batch, heat it back up until the agar fully melts, shear in a second amount equal to what you did last night, making sure it fully dissolves, then let it set again. I'm pretty sure that will work.

You can also pick up a sub-gram scale on Amazon for around $20. Thanks, drug dealers! They are very helpful when making small batches of "molecular" recipes.