Lots of Questions from Newbie Vivaldi User
1 - I can't agree more
2 - TBA, stay tunned.
3 - Tools > Show extensions > (down) get more extensions
5 - Not that I know of.
5. Not yet
6. True, the dark theme is better on such regard. Or you can try going to "Settings >> Tabs" and set either "Use page colour" or "Transparent tabs" (Option names may be different)