After looking at the “Pages” within the demo project, it does appear that there is some sort of indicator next to the page name showing which editor was used, such as “Contact us 2 – Elementor”. So that answers Question #1 and #2 in my previous reply. That leaves Question #3, which is:
3. Can I still use theme customize menu option and header builder along with Elementor? Or will Elementor overwrite the options I set in either one of these?
I think if this question can be answered, that should resolve this ticket.