I read your write up. I am in a same situation as you, working, family and stuff, so will need to do the heater core replacement project in multiple weekends.
That was the biggest frustration. I was afraid I’d forget or lose something. Labeling connectors and stuff and hardware in labeled ziplock bags were a huge help.
Just for the heck of it, I asked the shop that evacuates my a/c system what they would charge for a heater core replacement. If I remember correctly, it was $800 In 2018. I know shops may vary on that price though.