That battery temperature thing really confused me while testing as I put things back together. Makes sense it worked fine when I put back together after I'd had enough.
I found the finger print reader easier to put on after removing it from the case. My finger print reader didn't work after I put it back together. But started working the next day.
I found it easier to connect the motherboard to the daughter board when the daughter board is fixed in, then you just hold the motherboard vertically, click them together and tilt the motherboard back into place while using something to poke the flap connectors out the way.
Those two wires/ arieals? They loop under the motherboard for when the speaker goes back on.
As you're testing as you put things back together, the volume buttons only work when everything is screwed back in. I've come across this before on other samsung phones, killed me the first time trying to figure it out!!