So minus the part about it being too early, my fiancée did this. Her ex-husband was married previously with 2 kids and shared custody with his first wife. She would go to the kids' events and all but never to things like teacher conferences or anything like that, instead yielding to the mom. She'll freely talk about how it wasn't easy but she's also the most pragmatic person I've ever met and just figured she'd handle it.
Once she split with the ex, it got a little tough as while she didn't want kids, she of course became somewhat attached. To use her words, she's more of a mentor now than anything to the kids (now 23ish and 17 respectively).
We're actually going to see her step daughter later this month (and while I like the kids, it's such a strange spot being engaged to the step-mom, adding another layer to it all but we make it work). It sounds cliche, but it's the same for me now as it was for her when she met her ex-- yes you'll cross that bridge when you get to it, but the mindset that worked was just to roll with the punches and it'll come into focus.
Good luck!