Some tips (in no particular order):

ifixit has guides. They’ve been helpful. I did the SSD. I had to get my graphics card repaired (see my other post) and prices for replacement cards are terrible. Can practically buy one of these imac’s on CL for what the graphics card is going for online.

Oh man, this JUST happened to me too with the same iMac. This computer is pretty great. And it was also basically my biggest purchase around that time. Poor grad student “swimming” in cash from an internship. The video card is what crapped out finally. Learned that after taking it to a shop. Guy there diagnosed it…

I have a cat who demands and requires all sorts of attention, includes petting his cat belly.