I contacted the battery first, using the connector and cable as a reference point. I wanted to make sure the cable from the battery did not put any stress on the battery connector after I glued the battery to the case.

Easy does it. By pull carefully in a low angel, especially in the beginning, you prevent it from snapping. Do not yank it.

Instead of using a heat gun/hair dryer (I do not have one) — I used the coins trick, and put a kettle on top that I filled with hot water. I used water at around 80ºC. The weight of the kettle also provides additional pressure, making sure you get a good seal. To cool it down, simply add some additional cold water to the kettle.

Yes it is. Have a look at the iPhone Display Adhesive Replacement guide

The video show battery removal without taking out the taptic engine first. So, what is the recommend method?

I had to use a TR5 on the RAM cage. TR6 did not fit.

2018 and 2020 are identical machines. Apple only upgraded the default file storage. There is no such thing as a 2020 Mac Mini really.

This is the most delicate part of replacing the RAM. Be very care full when open the lid and removing the WiFi connector.