In addition to setting the startup option at the URL opera://settings/onStartup to "open a specific set of pages" and adding the URL chrome://bookmarks/, if you want Opera's window to start in full screen mode, you'll need to modify Opera's shortcuts to add the --start-fullscreen command-line switch.
For example, right-click on Opera's desktop shortcut, goto "properties", switch to the "Shortcut" tab and add a space and --start-fullscreen after the target command.
Example:
"C:\Users\yourusername\AppData\Local\Programs\Opera\opera.exe" --start-fullscreen