A:AnswerNo, there is no announced "Switch Pro". The hype was bigger than actual reveal. This is not worth it as its the same inners as original base model, in my opinion, unless you don't already have a Switch.
A:AnswerAll of the tech websites say that the pre-orders are sold out online. However, I have seen people saying that they were able to go to a Gamestop store and pre-order one.
A:AnswerThe Nintendo Switch (OLED Model) is 0.1 inches wider than the previous model. So, with that measurement in mind, things such as carrying cases should absolutely be able to accommodate the slight increase to width and will work fine. However anything that has a VERY tight fit, like some grips cases for example, might not fit this new model. Also, any previous Joy-Cons and controllers that worked on the previous switch should continue to work on the OLED Switch, since there was no change to any connectivity.
A:AnswerBy no means an expert but talked with Live Support earlier today asking them the preorder go-live question. Granted, take it with a grain of salt, their colleagues told the Live Support person this wouldn't be available for Preorder until 2 weeks before release (would be 9/24). I seemed skeptical about the answer but talked with someone else talking with Gamestop support and their support mentioned something very similar. Not sure if true but would be an interesting counter to preorder scalpers.