All of the above is true. Now, the opening date is “projected” for late fall of 2019 I believe, so probably more October/November. If all goes well.
As for the crowds, like someone else said – crowds unlike anything Disney has probably seen before. Star Wars has a cult following, that alone will bring in hoards of people. Then you have all the regular Disney folks (many on here), who have post-poned their trips for a couple years, waiting for the new attractions to open, who will suddenly start flocking back. Think of how busy Pandora was, and then multiply that, a few/several/many many times. Also consider how much smaller HS is than AK size-wise, so how much more condensed all those extra people will be, and you can start to picture the crowds. The overflow will definitely impact the other parks. I’m sure it won’t be 10s across the board or anything like that, but I also am sure there will be a noticeable increase across the board, that yes, is going to be long lasting.