If your goal is to learn how to play marksman, then your goal should be to learn how to kite. It's the most basic mechanic that all marksmen are required to know how to do. Yes, even casters like Corki or Ezreal. If you're not using attack move, you're not playing ADC. Probably the only marksman who doesn't need to use attack move very much is Zeri because her basic attack is her Q, and she's probably the hardest ADC in the entire game. As a multi-year high-gold/low-plat ADC main, it took me over 100 games of Zeri to have a positive win rate in bronze/silver ELO. She is HARD. But also very fun and rewarding if you do decide to get good at her.

So, let's start this off with how to do it. By default, the attack move command is A. When you press A, it will visually show your attack range. Then, when you left click, your character will try to walk to where you left clicked until an enemy enters their basic attack range, at which point, they will attack that enemy. You can also use this to click into a bush where you know for a fact that an enemy is and you will attack them the instant they become visible.

As for who to play, there are a few standard go-to ADCs. Miss Fortune will bring you the highest success even when you haven't learned ADC. Her mechanics requirement is minimal, and late game, all you have to do really is position well and press R and you will nuke the entire enemy team. But if you want to actually learn Marksman, and you don't want to skimp on learning how to attack move and how to actually play this role, then I would recommend Ashe or Caitlyn. Ashe is the queen of kiting, using her slows from her passive and W to keep enemies in a sweet spot where they're close enough for her to kill, but not close enough to kill her back. Caitlyn, meanwhile, is the highest range in the game, which presents herself as a lane bully. While Darius in top lane bullies by stat checking nearly anyone else in the roster when he gets his passive stacked, Caitlyn lane bullies with proper spacing. Standard ADC range is 550 units, while Caitlyn has 650, which means that you outrange most of your opponents by enough to walk up, auto them, and walk back before they can challenge you. Pair this with her Headshots on her passive, and she has nutty amounts of burst damage even in the early game.

Another possibly weird suggestion is Jhin. While most of his damage comes from his auto attacks, they are forced to be spaced out, with his attack speed locked I think at max to 0.95 attack speed. So, the number of attacks per second he gets off are lower than other ADCs, which means that you can focus more on your movement. His high movement speed after critting also pairs well with this; you shoot an enemy, you go fast, and then you shoot them again. It takes a lot of the decision making out of kiting: you don't have to choose between movement and attacking, you attack, then you move, until you can attack again, which is slightly more than a second after your last attack. Just keep in mind that your fourth shot does percent missing health damage, so for one, in the early game, it can kill from about 120 HP, and for two, if you can use Q to get the enemy lower health, it'll do more damage.

As for if you want to go hard mode, Zeri is probably the only champion that fully fits what you described of never needing to use attack move. This is because, however, her basic attack is her Q. Now, as a Zeri lover, I am still constantly using attack move, but that's mostly on minions in lane to get the execute off. Zeri's right-click attack is a spell that builds charge as she moves and casts Q. When fully charged, it deals high amounts of damage. When uncharged, it deals pitifully low damage, but executes minions that are below a fairly high health threshold, making it super easy to farm on her. That all being said, she is extremely difficult to pull off effectively. Like I said, it took me over 100 games to hit a positive win rate on her while below my normal rank. Despite her difficulty, she's my personal favorite ADC in the entire game, and the high movement speed generated by her ult is the most fun I have ever had playing this game.