Can I paint my subway tile ?
Here is one project that did https://www.hometalk.com/2899458/painted-subway-tile-backsplash
Here's a tutorial on painting ceramic tiles, such as subway tiles: https://www.youtube.com/watch?v=IjcYo_YA8Zo
Yes. I would recommend studying several projects and ask questions of the posters.
Yes, but use epoxy paint.
Ask the paint pros at the home improvement store for suggestions on paints and application tools.