1. We've already had 8 cards revealed. Safe to say the reveal season has already started. 2. As far as I have come across / read so far, it would appear that a free legendary is only available to pre-order bundles. Of course, that might not be the official case - they could still offer one to everyone (like in previous expacs). Just haven't seen mention of it yet.
Actually they give us an agenda with all the reveals when the reveal season start so i'm not sure it started already. Plus there often is a launching stream before the reveal period. I guess we'll have to wait until we get the stream date before the reveal season start. My guess is: stream monday 18 or tuesday 19 or even maybe late sunday to start reveal period on monday.
For the second question they often say in stream that we will get X packs + 1 free legendary. It will probably be the same for this expansion. But it's not excluded that they put this free legendary in the adventure since they changed a little their way to do. But 100% sure you'll get one free legendary without paying the bundle !