Tomorrow should see the first part of the burning of Teldrassil plot (and the associated War of Thorns world quests); the week after will see the second part of that, and the final week of pre-patch will allow people who have pre-purchased BfA to run the Battle for Lordaeron.
They don't need maintenance to begin these because it's just flipping a content availability switch; keep in mind that the last two expansion launches haven't involved any planned downtime at all on launch day. Of course flipping the switch can expose bugs in the new content and cause unplanned downtime or other disruption, as we've seen a few times in the past.
The new UI is a bit small on my 1920x1200 screen, so I played with the UI scale slider under advanced graphics settings until I found something that seemed to work okay for me. That slider seems a bit messed up, in that there's a "1" on the slider but it doesn't correspond to the default at all. Also, the world quest icons on the full-screen zone map are tiny, making them easy to miss.