Maybe there are a few people who do not have magic, but are extremely resistant to magic used directly on them. In order for them to counter magic on their surrounding environments, they would have an object that would make magic extremely unstable and unpredictable in their immediate vicinity.

I'm still working out the races, so making some more resistant to magic than others is a good idea. And magical artifacts that do wacky things are fairly common, so I don't see why objects that make magic unstable or unpredictable couldn't be in the hands of a nonuser or really any other character.

is magic harder to use the farther away you want to use it? For example is it harder to lift a rock a mile away versus a rock that’s right in front of you?

I actually hadn't considered this. What's come up in my draft so far is all relatively close range, so I haven't really thought about exactly how far magic can be used and how difficult that may become. Using your example, however, it would probably be easier to lift a rock that's right in front of you vs one a mile away. Since knowing is a big part of magic use, it stands to reason that I would have no problems moving this rock that I can see is going to be light/heavy and isn't obstructed by anything, vs guessing that the rock down the road is light/heavy, not obstructed, or even there at all. Thanks for bringing it up! I'll definitely have to put more thought into this!

Maybe make it so that every living being has the same amount of magical energy, just some species are more efficient at using it—making them more powerful (but with the same amount of magical energy).

Right now, I'd argue that this is already more or less true to Fayne. In my post I used adlyns and domani as my examples since they are on the very opposite ends of the spectrum. Using them again, adlyns have the highest affinity for magic while domani have the lowest. This doesn't mean that adlyns are all-powerful and no other magic user could best them, it just means that magic use comes easier to them than to others. Adlyns are half dragon, which is why their affinity is so high, but they're also very rare and generally lack skill because they rely on pure strength rather than strategy.

Domani, other the other hand are by no means incapable of magic; having the lowest affinity just means that they have to work harder in order to use it. Because it's harder for them they are the forerunners for "specialized crystal use" on Fayne. They wear a multitude of small marked accessories that store energy to be used only when needed. Also, while they aren't more resistant to magic, the trade off is that they're the only race that can actually sense magic in use/having been used, via their horns. They're one of three horned races, including adlyns, and are the only ones capable of this.

A skilled domani could easily kill an adlyn in a magic battle, no questions asked. Still, this varies from person to person; no one humanoid species is naturally better at magic than another, its just easier for some to pick up than others.

And as far as how much magic someone has, this is not only entirely individual it's also not really important. One human can be born with a mana pool of 100 while another has 250. Casting a small fireball could cost 25 mp normally. How a battle between them plays out depends entirely on efficiency and state of mind. Say the human with a higher mana pool recognizes that he has a higher pool, so isn't worried about losing 25 mp. The human with the smaller pool, however realizes that losing a quarter of his pool in one attack could be dangerous, and so works on being more efficient with his consumption. As his efficiency rises the cost of that fireball lowers. Now he only has to pay 3 mp for that attack. Our friend with the higher pool goes on to panic because he's running low on mp and his enemy is still standing. In his panic he consumes more than necessary to use that fireball, paying 50 mp instead of 25. Human with higher pool exhausts himself, losing the battle OR human with lower mana pool uses better attacks for less, wining the battle before his opponent runs through his own pool. I will say that I have considered the possibility of someone being able to up the size of their pool, but honestly I think learning to be more efficient takes care of that problem just fine.

Thanks so much for the food for thought, though!