Spraying Fall Seeded Orchardgrass

I sowed a field in orchard this past October and it's had a rough start to say the least. A week after sowing it had 4 inches of rain in 24hrs from the hurricane followed by 9 weeks of zero rain. It's around 3 inches tall and the stand is good for the most part. I just broadcasted 400lbs of 17-17-17 per acre to hopefully speed it up since we've had some warm weather.

I was planning on spraying it with 30% UAN in March and adding 24D to control the henbit and chickweed in the OG.
Is 24D okay to spray on smaller OG? Or should I go with something else?
Also how much N is too much? I've never been scared to put on fertilizer and was planning on putting down 30/gal acre of 30% along with the 400lbs of 17-17-17 which would give me just over 150 units of N.

Spraying Fall Seeded Orchardgrass