Generally they are 3-12 months in duration, although recently we are seeing much longer ones (24 months) from firms such as Citadel.
You generally draw full base salary, and healthcare comes from COBRA.
US-wide ban of non competes is good for hiring firms (they get the talent immediately), bad (allegedly) for firms from whom the talent is leaving, and mixed for the workers themselves (for whom the garden leave can be sometimes received as a paid sabbatical). It will be a really big change.
So for sure no "garden leave" if you quit, and also not if they can find a reason to fire you. And of course no bonus, which is often a majority of total comp.
Possibly this sort of thing may vary by state. There might also be some room to negotiate depending on how much they want you.
100%+ annual bonus for performance are not unusual and typically they are not paid during a period of garden leave.