I agree with the idea of taking it one year (or even just one step!) at a time. Yes, 142 is more than just a "little bit" gifted lol! OTOH, I'm not surprised your ds seems "normal" - lots of gifted kids, no matter how gifted, seem just like any other kid until you get to know the inner workings of their brains. We read a lot about the quirks and idiosyncrasies of gifted kids and hear all about how to deal with them due to them being outliers on the ability scale, but sometimes I think we can take that to an extreme. The 142-SB kid that you have today is the same kid you had 2-3 days ago before you knew the numbers on his IQ score

Re the impact of early reading - I don't think that will impact his IQ score one bit. It will impact reading achievement tests, but I wouldn't stress out about that. I also wouldn't anticipate that it will ultimately change where he will end up later in school re his eventual reading ability - it will mean he'll be working ahead in reading during the early years of elementary due to exposure and teaching, but I'm guessing by the time he's in 2/3 grade you'll see quite a few other gifted kids who are also reading far ahead of grade level whether or not they started reading at 2 or 6. Our ds12 didn't start reading until he was in K and even then he didn't let us know (he never would have put up with us trying to teach him at 5, much less 2 lol!)... but once he started reading it wasn't long until he was reading college-level books. We've never stressed out about getting him accelerated in reading in school - instead we've found that advocating for stretching him in math/science worked best *for him*.
Each of our kids is going to be different/individual. I've found that reading all I can on giftedness helps me to have a good bank of knowledge, but the real key is to just know my kids very well, inside and out, and take the cues from them re advocating for their needs.
Best wishes,
polarbear