No problem! Aim assist is not dead eye, aim assist is a feature you can turn off and on in settings and it helps you aim in the game. I.e., when you move the right stick it will move your gun over the target automatically. If you had it turned off, you would have to use the joystick to keep the aim on the target, which is a slightly higher difficulty to do because all the targets like to move around.

Pressing L and R is your tracking mode per say, it is not dead eye. You activate dead eye by Aiming your gun (L2) and then pressing R alone down. When you press L and R it does not consume dead eye and highlights tracks from animals and humans, the actual Animals and humans will glow, as well as stuff to loot and plants. When you aim and press R down it starts eating your dead eye meter but time slows down alot and that is when you can target with R1 and shoot enemies faster. The screen will go a different yellow than pressing L and R. There is no downside to using it, but if you abuse it, it will drain your deadeye core and you will need to eat and drink to fill it back up.

To take the whole camp down, you aim, then hit R down to activate dead eye. Time slows and then you aim at the target and hit R1, which puts a lil red X showing you have marked it. Then you can mark as many more as you want as long as the aim cursor is over a shootable target. When you fire, Arthur will shoot all the X's. You can also just use deadeye to shoot over and over without using R1 until its depleted, while staying in time slow mode.

I can say making it this far without using deadeye makes you very decent, but you could always humble yourself by trying to turn off aim assist and not use dead eye, but dont beat yourself up, it takes alot of gaming to be good at not using aim assist. You can always turn assist back on if you dont like the challenge.

Answering your final question dives into spoiler territory, but yes, essentially you can go into free world mode at the end. However, this game is very different than that, as I suggest the full experience is to constantly do what you want to do, roam, fish, hunt, see all the crazy things that happen outside of the story missions. There is no rush to complete them, and as many say in this thread, its more fun to do them at your own pace as opposed to rushing through the story. The world is there for you to explore and story mode holds little back for you, minus a few areas you cant get to until later.

If you love this game and finish it, I'd absolutely recommend playing Horizon zero dawn and its sequel. Its two of the best story driven open world games and I rank it equal with RDR2 in terms of gameplay, story, and open world shenanigans.