I don't think it's too long. I do think you are overanalyzing, which is understandable, but that might be making you put more weight into the introductory message than you need to. I'm more direct about a connection, and if you feel potential there then you should say what comes natural to you, instead of making yourself feel pressured.You don't think it's too long?
I get that you're like "holy shit, I have to say the right thing" and stuff, because it does matter and you're probably afraid of saying the wrong thing. I still think you should throw all that caution to the wind because the long term potential you see in her will play out, or not, no matter what you say. Write what you want to write, in the way you want to, and at the length you want to.