If you are using the Laptop layout, the default Orca Modifier will be CapsLock If you are using the Desktop layout, the Orca Modifier will be both Insert and KeyPad Insert, the latter being the same key as KeyPad 0.
Win + Alt + s = On/off
[Orca Modifier] + space = Prefs
[Orca Modifier] + Semicolon = Read all
[Orca Modifier] + Shift + Up = Speak current selection
[Orca Modifier] + A = Switch between browse and focus mode
[Orca Modifier] + Z = Toggle structural navigation
h = Next heading element (then 1-6 for levels)
Alt + Shift + h = List headings
[Orca Modifier] + Tab = Next form element
Alt + Shift + f = List form fields
t = Next table element
Alt + Shift + t = List tables
ALT + Shift + [arrow keys] = Table navigation
l = Next list element
Alt + Shift + l = List lists
i = Next list item element
k = Next link element
Alt + Shift + k = List links
Alt + Shift + m = List landmarks
m = Next landmark
Alt + Shift + a = List clickables
a = next clickable