You have to remove camera connectors and speakers to remove motherboard. The battery connector is kept in place by adhesive.
Too hot to touch is about 40-45 degrees Celsius. I recommend to wait until you get 40.
Temperature of heated iOpener should not exceed much above 140 degrees Fahrenheit or 60 degrees Celsius in order to avoid damaging electronics (especially battery).
What is the temperature of the iOpener after heating it up? Does anyone measure it?