We have a solution like those in posts #2 & 4; a connection to the entire breaker panel with a sliding metal interlock, top right inside the breaker panel. The generator breaker switch can only be turned on if the main breaker is switched off to allow the interlock to be slid up.
I have marked all the high power circuits with red dots so I can temporally switch them off prior to connecting the generator. Then I switch back on the ones that the 7K generator can support.
Wired to top left on the panel is an alert that line power is back on as we can't see neighbors houses:
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
Wired to center left is a watt meter that shows load on each 120v leg of the generator.
Wired in at bottom left and positioned about a foot away is a Reliance single circuit transfer box. We used that to power the furnace with a 2K Honda generator prior to the current setup. I left it wired in as a backup.