I'm new to Vivaldi and have just noticed that point 1) is configurable. Solved on my side.
Number 2) is just a suggestion - not something too important. I noticed that sliding left and right in Vivaldi in the tabs view mode has other behaviors different from what I was used in Safari but I just get used to the "x" to close tabs.
Number 3) is different from what you've mentioned. At first I thought it was that the same, but no. When using Vivaldi iOS, by sliding up and down in any webpage, the address bar either appears/disappears. That animation is the one that is laggy.