Yes. Hearthstone Access is completely free!
No. Hearthstone Access does not work on any operating system other than Windows.
When Blizard updates the Hearthstone game, Hearthstone Access is removed. You can try reapplying the patch; this works for small "data-only" patches such as balance patches, but will not be effective for large patches such as those that introduce new features or expansions to the game. Keep an eye on the Discord server and this web site to know when new updates to the patch are ready.
This issue is usually caused because a new event has begun and a splash screen announcing the event is obscuring the game field. To fix this issue, restart the program, go into the journal, and choose Event to launch the special event. If you do not see an event tab, send a message in the Discord server so we can continue to diagnose the problem.
You must repatch the game after a language change.
If you experience bugs, you can post about them in the Discord server. You may be asked to send debug logs to the developers. To do so, press Escape from within Hearthstone to open the Game menu, then choose options, and enable the debug logging checkbox. Then, do whatever causes the bug to occur. Then close the game and nnavigate to the location where Hearthstone was installed (usually C:\Program Files (x86)\Hearthstone). Open the Logs folder inside that folder and zip up the folder corresponding to the current date and time. Then attach this zip file to a Discord message.