You got some advice, I'll add more.
First, don't worry about jungling until you are level 10 and get use the Smite summoner spell. Without it jungling would be very unfun.
No for mid, you got some good advice, but I'll add my thoughts.
Ahri - very popular recently, She's not really an assassin, but can be very powerful. She's a bit tricky to learn due to her dash abilities, but will never be a terrible choice.
Azir - he was very good until a recent patch took away some of his damage. He can play relatively safe, but he's a bit tricky as he summons sand soldiers to fight for him. I've played with a good one and he was impressive.
Leblance - Mage/Assassin. She's one of the champions many people say the hate to play against, but that's because if she gets a few kills she tends to steamroll the enemy team. I can't say much more as I've never played her, but I've seen some good ones.
Lux and Morgana - Two very good mages that I put here together because in some ways they are very similar. Lux has a better ultimate ability in my opinion and is considered the more natural midlane mage. Morgana however is great at "farming" for CS and can also play as support thanks to having the ability to stun an enemy champ.
- These are all good champs. However, I do not recommend them for new players. Nidalee has 2 forms (human/cougar) and can be difficult to pickup. Syndra is another hard to play champ as she requires that you pay attention to the number of dark spheres in play. Cassiopeia powers up by poisoning the enemy champs, but is also not very mobile and is extremely mana-hungry. Orianna is another one where you have an item you manipulate with your abilities. She's fairly safe during the laning phase, but it can be difficult to direct her toy properly.
Ziggs - the mad bomber who reminds me of Crazy Harry from the Muppets. He's fun to have on your team, but is another mana hungry and squishy champion.
- Xerath and Vel'Koz - good solid champs. Not amazing, but not too difficult to learn to play.
Veigar - a recent change to his E ability has a lot of people upset as it made it much more difficult for him to stun enemy champs, but he's still a mage who can do a lot of damage to an enemy team. But he's also often a primary target for the enemy team to kill.
Zyra - I play her as support. She doesn't really have the ability to put out enough damage to excel in the midlane. I don't recommend her as a first choice.
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Also I see you worry about stealing kills or failing as support. That mostly depends on teammates. Most good ADCs aren't going to complain if you end up getting a finishing shot occasionally, especially if you keep them alive. Any many of the better ranges supports are all about poking the other teams champs while the ADC tries to kill minions, so it can be fun. It can also be boring if your ADC is going to hug the turret. I still recommend it as a way to learn more about how an ADC works, as you can watch one.
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Finally, although there are a lot of mages that go mid there are also melee assassins like Zed and Katarina. They usually will win that 1v1 unless you have practiced. Don't get too down on yourself if it does happen. Those two champs need to "snowball" to be effective late game so people play them very aggressively in order to try to get kills.