I wanted to suggest 1 and 2 as-well.
one thing tho is that i went to check, and the default force touch preview in Mac Os doesn't have round corners. it looks similar to the new Orion preview. but round corners was my first thought aswell
Agree. i would just have the default "fullscreen" button replace current web-view instead of opening in a new tab (like Arc). Then have a second button for open in new tab without going to that tab, Similar to "Open Link in New Tab" in the right click menu.
Reason why this is useful is that if you have a list of links that you need to go trough and figure out which you can use. its annoying being send to that tab and then have to go to back to the original tab to continue going trough the list.