So as of now, I main Ahri and am really liking Talon. However, I want to have just one more champion that I can pick mid as an option. I am considering Kassadin but I'm not entirely sure on him yet. I am also looking to get some options for a Jungle secondary role and for whenever I need to fill. Thanks!
Honestly, Ahri is a good generalist Mage and Talon's a good Assassin, you basically have your bases covered.
If you want to branch off of Ahri, focus on any one or two things you wish you could be doing better while you're playing Ahri. As a generalist, her only defining feature as a Mage is her mobility. Her burst is weak compared to a powerhouse like Syndra, her Waveclear is lackluster compared to an artillery like Xerath, and her sustained damage is nothing compared to a rampaging Cassiopeia. You should keep Ahri as your staple Mage for Mid Lane, and pick up more specialized Mages for specific occasions that you personally find Ahri lacking in. Or if you want another generalist, Orianna, Anivia, and Taliyah are pretty good if you're willing to put in the time for them.
As for your Assassin pool, you'll definitely want an AP Assassin like Fizz or Katarina. Zed is the obvious poster child for AD Assassins but he and Kat also take a LOT more mechanical skill; that's a lot of time investment for backup picks, is what I mean.
As for Junglers, it's my personal opinion that everybody should learn to play Nunu. He can do any Jungle route, his ganks are amazing, he scales great into the late game, and he fits in almost every team comp. After that, same deal with Ahri. Find out the things that you personally think Nunu isn't good at and learn more specialized Junglers to fit those needs.
You seem to like assassins and mobility. Kassadin seems like the perfect choice.
