How many rolls did it take you to get Okita?

Honestly? It's all pure luck. Some might got her with a single ticket or ten roll, others maybe didn't get her at all after a few hundred quartz.

You can't predict how many it will take.
To have a decent chance of getting a servant 600 quartz is an okay bet, but you can still get unlucky.

To put it in perspective, i got Illya in seven tickets when i was rolling just for the CE, but i didn't get nero bride in 600+ quartz.

I don’t remember the exact amount but I usually like having at least 400 quartz before summoning someone I really want. 400 quartz is 133 rolls which is about 61% chance of getting her. 300 quartz will get you a 50% chance for reference. But in the end it all comes down to luck really

It is bizarre really.
I've spent a small amount of quartz and gotten an NP2 servant, and then spent tons and tons of quartz only to never get another copy.
(like tons)
Yet with ~450 quartz I got NP5 Archer of Shinjuku.
(??)_(??)
It is really about getting lucky I think. But with 400 ish quartz you should (probably) be able to get NP1.
If you're only going for NP1 you can call it quits if you get her, but I personally usually go for NP2 if I can.