Hi bro, don't worry about nitrite actually, nitrite is not toxic in marine tanks even at fairly high levels.
But since you are monitoring nitrite already, then also since you are still cycling your tank, it is not a bad thing to see nitrite! That means that your cycle is moving on nicely.
As for nitrate, it is also very good to see it now, as that means your tank is almost completed its cycle.
Just let is be for a few more days and wait for ammonia to go to zero. Once Ammonia goes to zero, then your cycle is essentially complete.
I would do the water change only once cycle is complete, maybe even up to 50% since your nitrates are fairly high. Once that's done then congratulations, you can add fish!