Hi Logician,
you said
god that is omniscient would know all of its future decisions, therefore is severely limited by its own knowledge, i.e. has no freewill.
Omniscience means all knowing,..end of story (unless you have a different understanding of omniscience). There is no reason for making decisions since there are no problems to be solved, and this could hardly be described as a severe limitation.
This seems an absurdity, therefore, at best a god can only be omniscient about all things and decisions unrelated to itself.
I'm not sure that a non-omniscient being such as man can determine if the state of omniscience is an absurdity. Certainly it does seem to be an absurdity to postulate an omniscience and then attribute to it the limit of only knowing about 'things' and 'decisions unrelated to itself'.
But this means it is not truly omniscient, as it cannot know the future, since it does not know the actions it will take. If it is not omniscient, it follows that it cannot be omnipotent, as it is usually taken that one implies the other.
Now that you have postulated a non-omniscient omniscience, everything you say from here is not dealing with omniscience but non-omniscience. Let me remind you that omniscience means,...All knowing,...end of story,..in the rhetorical sense.