Is there objective Truth?

[Edwardo Piet]

Infinite would include eternal. If it has no beginning or end in space, it has no beginning or end in time.

Not necessarily. Eternal means without beginning or end; infinite means limitless in quantity, an infinite something can be temporally finite in the past.

Existence itself is external because existence itself has never been non-existent because existence itself is always existent because existence itself can never be non-existent.

The universe may not be eternal.

But only if it and its beginning is distinct from the totality of existence itself in all of its eternal entirety.

ETA:

I can as a point of awareness that takes up no space in a sea of empty blackness.

A sea of empty blackness is not no things. It's a sea of empty blackness.

But I cannot imagine no space at all.

True. And if you can't even imagine that which is a subset of there being no things at all then you certainly can't imagine no things at all.

And, of course, you can't imagine no things at all because you can't imagine nothing or no thing or not any thing or not any things. Because nothing isn't anything to imagine and so is hence unimaginable.

I can however imagine no empty/voided space if all of available space is taken up by mass/matter.

Anything you can imagine is a thing you can imagine and not no things or nothing.