Suspected that the HDD was failing so decided to go with a new SSD and replace the battery while I was in there.
It went swimmingly. It could not have been easier following the iFixit guide. The magnetic mat was a big help just keeping the screws tidy.
I was surprised at how little dust had accumulated over 3 years. I still cleaned it out a little, especially the bottom panel. It had collected some smudges over the years that some isopropyl alcohol and lint-free tissue took care of.