The easy, safe way is to get a transfer panel to switch loads. A Generac
kit can be purchased for 2-300 and instaled for apx 200, it is a
complete, wired kit. This way you have 6 circuits and can monitor watts
used.

Anything can work but if you have to ask, then hiring a pro is best. At
that point a transfer panel cost will still be ,mimimal.

An adverse problem could be not being sure you output 120v 60 Hz