When should I start talking to the GT coordinator and principle? He also just feel in love with reading, but nothing earth-shattering - captain underpants, Garfield, etc. I think I would rather he be double-accelerated in math to 5th (there is very limited precedent for this, but for older kids) that whole skipped in everything to 4th (which would not be an additional math acceleration). Or should I just let it lie and let the school do their thing? They were exceptionally accommodating in the spring and I don't want to press my luck.
When something new like subject acceleration is being tried, I think it's useful to all involved to keep in communication with the school if you think it's still not challenging enough. From your earlier descriptions, it sounds like the school staff is very supportive and wants to do right for your DS. I would go in very appreciative, but still let them know that you feel it's not quite enough yet. I wouldn't wait an entire year to let them know. In my experience, it took a very long time for any changes to occur, though it sounds like your school is pretty on the ball and willing to help. Since you have a bunch of scores now, I would ask if there are kids with similar scores in the math class your DS is in, or if not, are there more kids with those scores in the next class up.
I don't think you'd be pressing your luck if you ask the school's advice about what to do when it seems like the one math skip isn't quite enough. But definitely go in to a meeting saying that you appreciate everything they've done so far.
I am not familiar with Everyday Math, but lots of early elem curriculum seem to have a lot of repetition, and the trouble for HG kids is they learn something once and they know it, and they don't need to learn it 5 times. Pacing is many times an issue too - they need to go faster than the rest of the class. I'm just babbling now, but these are some things to think about when you're trying to figure out next steps.