Yes, groups of 2 and 3 are common. Four is less used, but present in nature as well: 4 cardinal directions, 4 seasons, 4 ancient "elements" (fire, water, earth, air), 4 phases of the moon. Five is also very common in natural objects: flowers, leaves, starfish, etc. There is symbology attached to many numbers.
As for deity, I do not find it reasonable that it would only be a trinity. Why only three aspects? The Muslims, if I recall correctly, speak of the "99 most wondrous names of God", but even 99 must be insufficient to describe the infinite. Each of us, however, will only encounter some of these facets durring our lifetime. It is a bit like the story of the blind men and the elephant.