Well for #3 there are a lot of things you can do. Why, it happened to me today! I told a girl I saw her walking, found her cute and just had to say hi. She said "thank you" and I proceeded to ask what she was listening to. See, one thing is you can just ask her about something she is wearing or using. Otherwise if she is walking you can ask her where she is going. If she is eating, you can ask her about the food ("I have never tried the burgers here, are they any good?").
Don't make it more complicated than it has to be

I think you have already done a lot just by opening them. It makes it clear that you're attracted to her and that you have confidence. Those are two extremely important points and you made them immediately with one phrase! Then it's mostly just about carrying a conversation to find out how she feels about you and if you have any chemistry.