Looks like this guide and the guide for the late-2016 variant of this laptop are essentially identical. I realized I had been using both guides about 3/4 of the way through working on my wife's 2017 model. Oh well. Might be worth combining them.

Definitely clean out the old adhesive. It's worth the time to have that clean surface for the new battery. Don't be afraid to completely cover the old adhesive in acetone to loosen it up (including around the edges), but don't use so much that it wicks everywhere...because it will. A steady hand, plastic scraper, tweezers, and lots of patience is important here. Especially patience. Put on some headphones and a favorite album and go to town.

I broke one of the plastic bits on the top left corner of where the middle battery sits. You'll know it when you see it. Snapped clean off. I left it out during the reassembly process, and haven't noticed a difference. Just be careful here, lots of fragile components.

This tip was a godsend. Despite my best efforts, some acetone still got under the speakers, but since I had to wait a week to complete the job (I damaged the new battery and had to order another one - user error 🤦‍♂️), I dried up what I could initially, then just poked at the speakers periodically over the week to make sure they weren't coming loose. No issues.

Looks like this guide and the guide for the 2017 variant of this laptop are essentially identical. I realized I had been using both guides about 3/4 of the way through working on my wife's 2017 model. Oh well. Might be worth combining them.

The washers really need to be mentioned before removing the trackpad. I pulled it out and excitedly showed my wife, not realizing that I'd just flung most of the washers onto the carpet. Luckily I found them all, but holy crap, please put this in step 22 or like 21.5, PLEASE.

This step would benefit from showing a picture of the black pads in question. Pic: http://i.imgur.com/zQnehtA.png

These are 3.0mm screws, not 5.0mm. This step could probably be condensed into the previous step.

- There are 14x 4.0mm black screws, but the step only shows 13 of them circled in red. One of the 11 orange circles (near front of unit) is actually the 14th black screw. Photo: http://i.imgur.com/7G64egd.png

- As for the 6.0mm silver screws, there are only 8x of those. The two silver screws behind the IO ports on the back are 3.0mm fine-threaded screws. Photo: http://i.imgur.com/cQD6KQu.png

- Source: Have a PS4 Slim (CUH-2015A) right in front of me, doing this exact job. Hope this helps someone else down the road.