My friend, you have misunderstood omnipotence. God is omnipotent, but let’s clarify. First, can you concieve of a four-sided triangle? If yes, that’s incredible, if no, that’s correct thinking. A triangle is three-sided, and to say it is both three-sided and four-sided at the same time, and in the same sense, is to say there is a contradiction in its nature, as if it refutes itself. It cannot exist in this way. It is necessary for a triangle to have three sides in order for it to exist as a triangle.
Think now to God. Omnipotence is the ability to do, or cause, or effect anything that is possible. To ask if God can make a four-sided triangle should first be preceded by the question of whether, or not, a four-sided triangle can even exist - the answer of which is no. Such questions are broken in themselves.
Now, transfer that principle of the triangle having three sides as necessary to exist over to some of these questions you’re asking.
Can God be nothing? Well, if God trancends time and is eternal, when would He not exist? If being God means being eternal, how could God ever not exist? If God is God, won’t He alsways be God? You see? It is necessary for God to always exist in order to truly be God. No infringement on omnipotence here, He is just doing what is possible only for God and no one else.
Can God be bad? Do evil? Well, if God is God, who would judge Him? Are there any moral standards that are higher than Him that He must appeal to? You see? God could not be God if He wasn’t the ultimate stadard for morality. Who else but God alone could do that?
Can there be someone equal to God? Yes, and no. If God and God were in a competition, Who would win? Neither. They’re both equal in their ability. Let’s say my fist is an unstoppable force, and the punching bag is an immovable object. You cannot have these two seperate entities existing at the same time. It’s in the very nature of my fist to be unstoppable, but if the punching bag is immovable it will stop my fist. Therefore, it is not possible for two seperate Gods to exist. However, if you are a Christian, you know that God is a community of Persons, Each having the divine essence in its fulness with no division among Them, distinct only in Their particular personhood. They are not at odds with one another, but are Each in absolute harmony with the other Two. In this way, the Father, Son, and Holy Spirity are each fully divine, and of the same divine essence. Also, if to be God is to be the eternal first cause, when would this other God begin to exist? And wouldn’t being created mean that you are definitley not God?
Basically, it is only good sense to say that some things just aren’t possible. Thank God this is true. It means that things can make sense.
Hope this helps. Praise God!