reasons for entities other than the creator and the Law of One

[Siren]

Why create other entities?

...what sort of entity do you create in terms of memory, knowledge, and individuality?

You don't create "other" entities. It's just You all along. You don't create anything externally or internally to You, really. You Is All There Is. You only discern upon the concept of many-ness and the limitation of your own Infinite Awareness via a set of progressive illusory experiences, in order to explore Yourself, know Yourself, (re)discover Yourself, in a sequenial fashion; thus recapitulating Your own "coming into being" or "awakening" of Your own Infinitude.

You actually lose yourself, forget yourself, to find yourself, remember yourself.

Dis-member to re-member, get it?

Thus, after free will, what other attributes would a truly great companion or set of companions have?

Hmmm, truly great attributes...?
Duality. STS and STO, for a change.
Thus we may better understand Our Unity.

The veil and free-will, as others have said, serves to purify our intentions - so that we pursue a path of love and light not in some utilitarian calculus, but so that it is an inherent part of our being.

The "veil" and Freewill serve as a catalyst to create a greater and richer variety of experience. It allows STO and STS to come into play.

Surely even the creator must be moved to tears by the sight of his children finding the same beingness and path of love and light at which he exists, for themselves, without his direct intervention.

The Creator is only playing with Itself in this Grand Cosmic Drama. There really are no "children." The Creations and creatures you see around are not "part of" the One Infinite, they are, each and everyone, the same One Infinite Creator.