Psalm 82:1, Elohim can't be standing in the midst of one elohim.
Depends on how we define the distinction and unity of these other beings.
Lets say God had a wife, Asherah exists. Is she then one with God the same way as the three to make her God? Generally, Trinitarians require members of the Godhead to have a certain relation (e.g. familial relations, dependence relations, or compositional relations) creating an ‘indivisible unity’ such that it is impossible for anyone person to function as a God without the others (e.g. Jesus must mediate between us and God the Father). For the Creedal Trinity, God is undivided by "substance" or "essence", then there is the Social Trinity where God is undivided by "purpose" and "will", that it's justified to reference them with a lack of distinction.
Or like Kabalistic Judaism, the ten Sephiroth, angel-like attributes of God's personality. Each are just different "Aspects" of God. It's a very interesting idea, a little better explanation of the sort "tether" that binds the triunion of the Trinity when they each have independent wills. Not my favorite concept, but one possible interpretation of reality I can't disprove. What if all angels or all of us are just aspects of God's own mind? I can't put down monotheism absolutely in that case, even if the 70 extra gods of the nations exist.
"There was Eru, the One... the Ainur, the Holy Ones, were the offspring of his thought" (J. R. R. Tolkien – The Silmarillion)
Thanks. I still can’t see from your post whether or not you believe that there is a case for God himself probably being more than three.