[Details inside] Can you give me some advice for this sticky situation?

Sorry if this gets long.

There’s this guy who’s been coming to my church for about 3 years. I don’t know much about him (largely because no one will talk about him), but he gives me the heebie-jeebies.
Here’s what I actually know.

-He lives in a group home.
-He’s had problems with addiction and his anger in the past.
-He works in a “supported employment” program, PHASE.
-He doesn’t have a driver’s license and calls my dad once every week or two for a ride.
-No one in the church feels comfortable giving him rides (and they won’t tell me why). They’ve told my parents specifically not to give him a ride with my sister and me in the car.
-None of us know why (and if they know why, they won’t tell me), but none of the girls in the church are allowed to talk to him.
-He has personal space issues and is generally awkward.
-One day a few months ago, he came into the store where I work (on my day off). He asked several people about what I do for work, when I work, and even asked one gal if she knew where I lived. Obviously, no one gave him any information, but he did confirm that I still worked there. In the few months since, whenever he sees me, he asks if I’m still working there, and says he’s going to “come visit me”. <<internal cringe>> My coworkers say they’ve seen him in the store several times since then, but I haven’t.
-One day last summer, I was running an errand for my boss, and we happened to run into each other. I brushed him off very coldly, saying, “I’m very busy,” without slowing down or hardly looking at him. I didn’t look back to make sure it was him, but I’m fairly certain I heard his bike behind me for a few blocks.
-I cringe at the idea of drawing a conclusion on a person’s character from this, but it has to count for something: My heart starts pounding whenever he talks to me, especially if I’m on my own. Adrenaline kicks in and I go into fight-or-flight mode. I just have to get away! I’ve even hung out in the women’s bathroom to avoid him.

So here’s what I wanted to ask.
1) Am I justified in being so creeped out by him?
2) Last week, he found out my work hours. I have to work tomorrow, and he said he’d be “visiting” me. If your answer to my first question was yes, why? What kind of problems might he cause me? Would I be justified in asking my boss if I could work in the far corner of the store, where this guy would be less likely to see me? I definitely don’t want to be stuck alone with this guy.
3) I have a feeling people in my church know more about this guy than they have told me, and they would know if he’d be a problem for me at work. Should I just be more persistent in asking them about him?

Am I overreacting?

And yes, that did get long. Sorry about that! You so rock if you read through all that.