We'll have the ability to share important news regarding scheduled maintenance and unplanned outages within the client, in addition to updates on the official Discord. We'll post patch notes in the Discord and on the official website--it's likely you'll find them elsewhere, like here on Reddit, as we have an active community.
As for a PTR, Stormgate will be entering Early Access, so everything in the game is effectively trying new things. Running a separate PTR while a game is in Early Access doesn't feel necessary as this is an active development phase and we'll be making many changes based on player feedback.
As for offline mode, our game is going to require an online connection when we release, but we do have plans to introduce offline support for single-player campaign at some point in the future.