OP: Can all three of these character flaws be resolved?
OP: Is there a general rule to determine how many character flaws can be fixed?
No, it all depends on how clever you are in the introduction of the character, inventing the flaws, connecting them, and inventing the journey of the character in the novel that gives her the experiences and epiphanies to grow and overcome these flaws. And how realistic you want her to be.
Now to your specific example:
a paranoid(1) loner(2) suffering from addiction(3). Assume those are 3 distinct problems: The larger mental health issues resulting in paranoia symptoms,
Stop right there. This is non-sensical, they aren't three distinct problems if they are linked, you bring up "larger mental health issues" that resulted in all three of these! How are they distinct? You are contradicting yourself.
Assume also that the external conflict is unrelated to the flaws. Maybe this person has to care for their parent suffering from dementia.
Why? Or perhaps I should say, fine, you made this job easy. If the conflict is not related to the flaws, the flaws are just a disability the MC does not have to overcome at all. They get in the way, sure. But for example, a murder detective paralyzed and bed-bound doesn't have to overcome her paralysis to solve the murder, it is just a daunting complication she has to work around to complete her mission.
Disabilities and flaws unrelated to the central crisis do not have to be overcome.
They can get in the way whenever you want, and if you strive to be realistic as an author, can get in the way when you don't want, and make your story more complicated to write. Those interferences can influence the plot, and make your job of inventing actions to lead to your desired outcome far more difficult. But you don't have to overcome them! Superman never becomes immune to kryptonite.
Your drug-addict hero may be stoned and get captured, or miss an important meeting.
Now, if you want the MC to overcome their flaws, then you have to be sure your flaws don't produce an irredeemable MC that most readers cannot forgive. Is their flaw a pedophile murderer that forces children into pornographic acts and then kills them? Forget it, that is an extreme case of irredeemable. Doing irrevocable harm to other people (like maiming them or killing them or coercing them into such acts or acts they will not plausibly forget) out of purely selfish interest (money or pleasure) is my definition of "evil", and permanent harm (mentally or physically) is what can make evil irredeemable.
Personal flaws, harming nobody but yourself, are redeemable, and correctable. Paranoia is often correctable, as is drug addiction, and even being a loner.
Off the top of my head, other correctable and redeemable flaws: Being an asshole is correctable. Depression and apathy and carelessness are correctable. Promiscuity and infidelity are correctable (although the latter might not be forgiven, an unfaithful MC can overcome, with someone else, their issues with remaining faithful). Being a thief or liar is correctable.
There are no limits to "how many flaws can be overcome" other than your ingenuity in devising plausible scenes that link together and make sense to the reader. I'd definitely try to link them together, so solving one meta-issue leads to solving multiple individual issues. For example, a lack of impulse control can plausibly lead to promiscuity, infidelity, drug addiction, irritability (being a jerk) and petty thievery. Getting a handle on the impulse control makes all the others easier to overcome.
Often, in stories, the crucial point of change for an MC with flaws is when one of these flaws is about to result in an irredeemable offense: Permanently harming someone, or doing something they themselves could not forgive themselves for doing.
As an example: In "Flight" (2012) Denzel Washington is a pilot, an alcoholic, a drug addict, a liar, a jerk, a cheater, his son and wife are estranged and hate him. None of these are causing any serious problem for him, he has a love life, he enjoys getting high and drunk, he gets his job done without causing anybody harm.
Then the plane he is flying has a mechanical problem and is going down hard. He saves (legitimately) a plane load of people. A hundred+ survive, but seven die, including a stewardess he was in love with. But in the investigation it turns out he was drunk at the time with cocaine in his system. After legal wrangling the blood evidence is thrown out and he is about to get away with this. He can make it all go away by slandering his dead girlfriend, on the stand and under oath, in front of the world.
That is what he finds an irredeemable act. He loved her. He can't do it, and confesses he was drunk and stoned. The save was truly legitimate, his flying saved a hundred some-odd lives, but he was drunk and high on coke when he did it.
In the movie he is redeemed, goes to prison for a few years, overcomes his addictions, repairs his rift with his son. That is a nice happy ending, but the climax was brought about because when provoked to what he felt was an irredeemable act, he broke.
So if you want to write a story in which the flaws are overcome, I suggest devising a story like this: The flaws are manageable, they are harming themselves more than anybody else, but eventually the flaws lead the MC into being forced to choose between an irredeemable act (in their eyes) and facing up to their flaws, and they choose to face up to their flaws.