Your project saves automatically, so you can close the tab and return anytime. Settings don't auto-apply to newly added tracks.
Your project saves automatically as you work, so you can close the tab and come back later without losing any progress. When you return, your session will be right where you left it.
No. Effects and settings need to be applied to each new track individually. Adding a track to a project you've already worked on doesn't automatically apply the processing you've done to the other tracks.
No. Saving happens automatically in the background, so there's no save button to remember and nothing to lose if you close the tab.