Did God, in His omnipotence, allow Satan to fall from grace have something to do with His allowing Adam and Eve to fall which provides first hand knowledge to the elect angels / elect humans in a way that our limited minds can understand? Is this an opinion that is consistent with reformed theology?
Correct me if I misunderstand, but I think you are asking 'Is the Devil's purpose meant to help us understand X? Where X is various ideas as understood by reformed theology. Reformed theology has a 'system of understanding' to view many of the events and persons you mention, such as the Devil, pre-destination, the fall, etc. and does support your concept that we can't fathom the purposes and mystery of God's will in them. Reformed theology also supports the fact that what God has put into his word truth about these subjects, in order to 'sort of' provide 'first hand' knowledge about them, but it would never understand the 'actual purposes' of those events and persons simply to communicate 'first hand knowledge' of the reformed view of them. That would oppose reformed theology directly a sit places the purpose in men, or their understanding.
The purposes of these things are bound up in 'God's glory' under reformed theology and transcends humanity, or our understanding of them, even in their orignal purpose. Everything was done from, through and to God's glory. This is reformed theology. Our understanding of them plays a much smaller role. However, it is also consistent with reformed theology to recognize God's glory as that which has been manifested to us in Christ. So you seem to be circling around the right concepts just not yet fully arriving as a settled position in terms of reformed theology. One key to reformed theology is to move the attention away from self, including our understanding, and move everything to God in Christ. Then understand that when Christ has all the attention it is the best, glorious and most blessed truth for us.