austrian_slinger
Welcome to the forum!
If I might share my outlook on the aiming thing...
Aiming is primeraly a function of the instant of release. Secondly, a function of body movement toward the target, done by the hand / arm, and sometimes a short step. Thirdly, it is a matter of knowing at all times exactly where the stone is. All these things seem very obvious, but sometimes they are not.
Whatever style you decide to use it will take lots of pratice, but you can shorten the time required to get fairly accurate if you will keep in mind that in reallity you are trowing a rock with your arm / hand using the sling as an extension. (That sounds like another Duh statement, but it is not.) ALL the control is in the arm / hand and NONE in the sling. So as you begin a throw you need to learn to "FEEL" where the stone is at all times, this allows the brain to figure out the exact moment of release. You just have to "let" yourself react correctly and at the correct time.
All this sounds funny, but slinging is very instinctive in nature. We humans are blessed with an absolutely amazing brain capable of calculating the release to the micro- second, in addition to figuring your stance, distance to the target, weight, shape, feel and speed of the stone in the sling, and a hundred differing bits of data, and do it all CORRECTLY! Once the brain has enough data, that is enough stones thrown, the next step is to train the body to do what the brain tells it exactly and smoothly.
I wouldn't get to hung up on absolute accuracy at first, just start slinging and having fun, and let the accuracy happen as you try different styles. If it ain't fun you ain't slinging right!

Anyway hope that helps. And welcome aboard.
WalkingBird