I should mention I am more on the side of the NeoPlatonic thought of Saadia Gaon. Just saying.
That is to say though I respect the Rambam, I am not committed to the idea that he was right about everything. Most Jewish thinkers before him and after him were more along the lines of NeoPlatonic thought and that makes sense to me.
The way I understand God is certainly along the lines of Saadia Gaon and the Rambam as being the First Cause and totally different than the world. That is Monotheism, not pantheism. But furthermore he is the cause of existence not existence itself.
[I am also suggest that the Rambam was less in the direction of Aristotle than most people thought he was. But that is a subject for a different time.]
Now Kelley Ross has also criticized Thomas for making existence the first property which is not even Aristotle. But furthermore I would like to express a different critique: that is "אהיה" means "I will be," not "I am." For example, if I want to say "I am in the store," I say "אני בחנות." I do not say: "אני אהיה בחנות."
"Ego sum, qui sum" isn't "I will be," it means "I am." "Ego sum" is I am present tense. "Ego" is the subject. "sum" is present tense "is."
"Ego sum" is present tense Latin. "I am." It is not the same thing as, "I will be" in Latin which is "ero." So a more accurate translation closer to the Hebrew would be Ego ero. As in ego ero victores I will be victorious. But for some reason the translators decided not to take that venue.
I am not saying Aquinas based himself only on a mis-translation. He had other reasons for his taking his approach. But I think all Jewish Philosophy in the Middle ages was simply and plainly neo-platonic and for good reasons that became clear only much later in Kant.
That is essence precedes existence.
I should mention that these are important issues but for some reason the Talmud and all books of the Sages ignored them. The first time Jewish though on these very important issue was expressed openly was with Saadia Gaon and the Chovot Levavot in the first volume שער היחוד.
After the Rambam Crescas and Joseph Albo attempted to return to the more neo Platonic approach of the Geonim.