Possibility to select text in link, not only drag link (mouse left/right - select, up/down - drag)
Use this extension. (Click "View raw" to download the file then drag the file into Opera's extension manager)
Tab navigation settings (Windows-like in order of use)
enable opera://flags/#activation-order-tab-cycling
Built-in browser proxy settings
Answered above.
Ctrl + left mouse button to save image
Use this extension.
The rest isn't doable right now.