Change focus within a grouping by holding ^⌥ (Control + Option) and pressing the ↑→↓← arrow keys.

When creating a new floater, link it to a side of the currently-active floater using the arrow ↑→↓← keys

This will link the existing floater with the new one in a grouping. Alternatively, you can press various other keys to skip linking and instead place the floater in a specific position on screen.

Arrange grouped floaters into rows or columns

Press ⌘⌥R (for rows) or ⌘⌥C (for columns) to arrange the current grouping's windows. Throw in the Shift Key (⌘⌥⇧R or ⌘⌥⇧C) to evenly stretch the floaters across the entire screen.

Hold Command and Option (⌘⌥) while dragging a grouped floater to unlink it from a grouping.