Hi James, thanks for the opportunity to contribute.
Q: do you typically launch a new tab before opening a bookmark, or replace the existing tab?
A: Both: if “a subject of current interest” tab is already open then => bookmark, otherwise => new tab => bookmark.
Regarding a solution to the real estate problem, you already have one on this page 
In other words, why not:
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Replace all the functionality you took away, the bookmark hamburger icon and my beloved Bookmark Bar [I love the ability to embed menus in it]
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Provide a means of alternately retracting/exposing all the controls (the URL and everything) by the user tapping on the two white lines in the centre of the orange bar.
- It’s intuitive
- users can choose from moment to moment whether they want to be navigating or reading
- it adds only 1 level of indirection, a small price to pay for instant access to a non cluttered and clean “user interaction” panel
- it allows future additions as you foreshadowed
- you avoid the coding complication of saving and restoring preferences and the user complication of setting them
- it provides the best of both worlds … a nice clean full screen plus maximum user interaction interface
Regards,
Phil