On tab position, here are a couple of Opera extensions you might want to consider.
Tab Position Options, https://addons.opera.com/en/extensions/details/tab-position-options/?display=en
Classic Tabs, https://addons.opera.com/en/extensions/details/classic-tabs/?display=en
You can save a session, if you have its tabs open, by right clicking on the tab, and then choosing to save them all, that is, "save tabs as speed dial folder." Then you can, if you like copy them over to a bookmarks folder. It's your choice how to store them for reopening.
Also, you can set Opera to Open where it closed last time (picking up all of the open tabs). Just go to alt P (settings), and for Startup, put a check in "Continue Where I Left Off."
If you want something more sophisticated, there's the Chrome extension, SessionsBuddy, https://chrome.google.com/webstore/detail/session-buddy/edacconmaakjimmfgnblocblbcdcpbko
To download a Chrome Extension, you do need the Opera Extension, Download Chrome extension https://addons.opera.com/en/extensions/details/download-chrome-extension-9/?display=en Or Extension Source Viewer https://addons.opera.com/en/extensions/details/extension-source-viewer?display=en
You can try the extension, and if you don't like it, just uninstall it.
