Being flirtatious IS normal. It's normal good social skills. Keeping things light. Injecting some woman to man into the conversation.
And messaging is just messaging. It is largely a drain on your valuable time.
Where it's at is spending time with them in person. Then spending time apart - preferably where you're not bothering each other a lot. Then spending time together. And so on.
That's a great way for building love. Great times together. Then time apart when you get on with your life and allow them to miss you and yearn for you.
Not being flirtatious would be kind of weird. As that would be putting on an act. Or being too serious. Or being in too much of a job interview mode.
It seems like the answer to being flirtatious over text in this context is to move the conversation on to meeting up in real life.
And then on the date it's fine to keep things light and flirtatious, whilst also getting to know each other as people, which will involve things like you telling anecdotes where you're vulnerable.