About the only time I like footnotes in fiction are for historical fiction tales that use the footnotes to tell you all the cool little true tidbits that are woven into the narrative. But for a 100% original world this doesn't really exist, so unless you are apeing a specific real world book in a scholarly or mockumentary style, I think expositionary "flavor text" of this type should be put into intro quotes at the start of chapters, clumped into an appendix, or doled out in interstitial mini-chapters (this is pretty common in sci-fi for the highly technical infodumps necessary).
Now an "annotated" book with your personal comments or factoids as a 4th wall breaking coversation with the reader would be cool, hopefully that becomes possible on the kindle. I would want to be able to hide them completely for a distraction free first read through, then I could go back to see what you had to say about specific areas or do a second read-through with the "commentary track" on.
But nothing is as bad as the "while our hero battles for his life agains tthe ravenous undead hordes, let us digress for a moment about the founding of the empire and why exactly the king always wears yellow on the 3rd tuesday of the month...."