Is it normal that i over think friendships?

So I tend to over think little things that probably most people don't even notice. Like it's so frustrating when I want to become friends with someone because before I even talk to them I start to observe their body language and what they're like, then I start to think of a way to start talking to them to a point where I make this plan a about the situation adding a backup plan of what I would do if things didn't work out the way they were supposed to. I start making a dialogue in my head and the worst scenarios, and then I make a pro and con list of why I want to be their friend. Like is this normal? Like it's not with everyone I meet, but like I tend to choose a few persons that really caught my attention and since in my eyes they seem like really amazing and stuff I get obsessed with being their friend even though we've never really met and talked. It's so frustrating because I tend to care way too much about those kind of things because I'm afraid that I might do or say the wrong things, while they might not even notice or know about me and wouldn't really care about those things. Like it's really hard for me to just do things out of an impulse and don't care about what might come from it. It's even worse when we already have made eye contact once or twice, like I get super paranoid about what they might think of me and the sightless thing they might do is crucial like I instantly think that they did that because they find me annoying or weird or they don't like me or anything. Like right now I'm debating over the fact if I should add this girl on Facebook because when she seems me around school with her friends they always whisper and stuff so I think they're making fun of me or judging me. I don't know, maybe I'm wrong, but I keep thinking of what would happen if she ignored my friend request or if things got worse and she thinks I'm even creepier. Like I know people add each other on Facebook all the time, even if they don't know each other, and it's no big deal, but it is a huge deal for me, and I know there's more people out there to become friends with and that maybe she wont end up being worth it, but I just really want to be her friend and I care too much. Is this like normal?