Man in some ways I think you're being too much and in one way I get you. I'm also an over thinker and analyze the shit out of everything, which is why my posts are also TLDR. I would also analyze every interaction and smile I get from a girl I like even if I had lots of experience before. The reason I don't do so much anymore is because there's a lot of other things going on in my head and I also have more than one woman who's on my radar. Just don't have the mental bandwidth to think too much about it.
When I mean mysterious, I don't mean being mysterious for the sake of it, although some space between people is healthy. Living a life full of things that interest you makes you automatically interesting. But you say you're living the way that makes your life feel full, then you're good. That's more important than having a woman, because woman are ultimately an accessory to a good life, not the goal.
From my personal experience, whenever I had the feeling a woman likes me, I was usually right. They make it extremely clear that they're interested, or they sometimes outright make a move. It's possible that your deli girl is toying with the idea.
But how much a woman likes you is very contextual. Women are much more fickle than we are. For us a hot girl is hot whether she's playing tennis, cleaning the toilet, or in her pajamas watching TV. A woman might find a man attractive when he looks like the boss on the football field or killing it on a speech, but then get the "ick" when he doesn't know how to replace a tire or something. I had women who were crazy about me but then get lose attraction for me when they see me everyday in my daily life, watching sports in my underwear, taking shits, not knowing how to do stuff, and overall seeing me be a normal human.
I also had several women change their plans and spend a lot of money to fly over to me, buy me dinners, go on adventures together and fuck me crazy before leaving teary eyed. These same women would probably lose attraction for me for one fuck up lol.
Overall I think you have a good attitude about how you want to love someone. It's noble to love someone without expecting so much back. But at the same time, it's a bit too much to want to give so much to someone you don't know. She could turn out to be a shitty person and take advantage of you. Watch out man. I've seen too many guys fall in love to their downfall, including myself.
If you're going to say anything in that letter, I would recommend only saying it under one of the two conditions:
1. When you already have her. It's cute to tell her how much you were into her when you're already together.
2. You're saying your peace and leaving her alone for good.