No research, just my personal opinion: borderline personality disorder.

alternating between high positive regard and great disappointment

First the stalker is obsessed by the person because the target is the most awesome person in the universe. Imagine a person who could give you infinitely many utilons, if they wanted to. Learning all about them and trying to befriend them would be the most important thing in the world. But at some moment, there is an inevitable disappointment.

Scenario A: The target decides to avoid the stalker. At the beginning the stalker believes it is merely a misunderstanding that can be explained, that perhaps they can prove their loyalty by persistence or something. But later they give up hope, or receive a sufficiently harsh refusal.

Scenario B: The stalker succeeds to befriend the the target. But they are still not getting the infinite utilons, which they believe they should be getting. So they try to increase the intensity of the relationship to impossible levels, as if trying to become literally one person. At some moment the target refuses to cooperate, or is simply unable to cooperate in the way the stalker wants them to, but to the stalker even this seems like a spiteful refusal.

In both scenarios, now the stalker feels hurt and cheated, and wants revenge. Projecting their false beliefs on the target, they believe the target has lied to them about the inifinite utilons; they blame the target for starting this whole process, and for destroying the stalker's life. (In the next mood swing, the stalker may offer forgiveness to the target, if the target agrees to give them the inifinite utilons now. Then they become angry again, etc.)

But maybe there are more possible mechanisms than this one. Also, my model does not explain why the stalker is targetting one specific person instead of multiple people, or everyone.

To what extend is getting a stalker a risk worth thinking about before it's too late?

I think it is worth thinking about, but I am not sure what specific advice to offer except for (a) avoiding everyone "weird", which seems like an overkill, and (b) using a pseudonym and other methods of protecting your privacy if you want to become even a bit famous.

I would certainly recommend to everyone who wants to become famous (as a bloger, singer, actor, etc.) to choose a pseudonym, stick to it, and never reveal anything personal. (Probably not even the city you live in; I would imagine that the idea that you are geographically distant would discourage most possible stalkers.)