Referring to someone you just met as “hun/sweetheart” seems borderline creepy to me. It’s too superficial. If I received this reference towards me in a text before even a second date, I would not answer, or if I answered I’d let the guy know “thanks but no thanks”. Perhaps that’s just me. Instead, in the first text you can just refer to me by my name. Subsequently, you don’t really need to address me directly, just say “Hey” then continue on with your text. After a couple of successful dates (meaning you were both smiling and/or laughing at times, and both seemed to enjoy the dates) the nicknames and cute references like “sweetheart” will feel more natural and fitting.
A lot of these one liners are really good for text messages, but you really need to do a lot more than just a one liner to set yourself apart from the rest. Remember, today’s dating world is fiercely competitive and guys are up against a lot of other guys competing for the same girl all because it’s so convenient to get in touch with one another. Online dating is just making the situation even worse, when anyone with a selfie can sign up and get spammed by hundreds of suitors in a few seconds. Keep these in reserve for after you get to know someone. The funnier ones especially: who doesn’t like to laugh?