No it's not creepy at all but really sweet. You can text her that. A guy once texted me something like "What you doin besides thinking about me?" and I was like he was thinking about me. Just do it now.
Well if you are friends with her then it would be OK, but I wouldn't say straight up "hey, just thinking of you" that would be weird, but if you are dating then its perfectly fine, just try and use different wording
I personaly say not. if your dating then she will know your think about her becouse you will invite her out on a date... she her affection when you see her and your with her, don't txt it.. if you must then call her and let her know but like I said I personally wouldn't do that.
I don't think it is too strange to say you are thinking about someone. I do understand that you don't want to give her too much attention too. You don't really need to say that you are thinking about her because if you are sending her a text you most certainly are thinking about her. All you really have to do is be engaging and that is pretty easy. link