Hello,
Take my apologies for the delay in answering.
1) Use the multiple header option https://youtu.be/BpeXfzNwkOc to create transparent headers with the overlap effect for some pages only. Watch the video tutorial, try to create the additional header for your page, and let me know if you still have additional questions about that.
2) If you want to use the custom navigation for the Revolution slider that we used on our demo then keep FA icons enabled in Theme Options > Speed Optimization > FontAwesome Support.
3) I imported the Medical slider for you and also added page custom CSS that was missing on your page after the page content import. Check styles now and let me know what other things you still need for that.
4) There is no migration tool from the WPBakery to Elementor. So, you will need to create page content from scratch if you decide to change the builder. That’s why it’s important to decide which builder you will use at the very beginning of the dev process to avoid creating from scratch again.
Regards