After a long day of writing two days ago, I managed to get the second book, Omen of the Ancient, ready for the beta reading stage. I also have one reader right now, and plan to get a second one when I can get my first round of feedback. I noticed with the first book that even just two beta readers at once can be redundant so long as the same issues are brought up, and I'm not constrained by time, either. Having one reader at a time should be enough so long as improvements can be made after each read. This is doable since the second book will end up being the shortest in the series.
I'm also considering making Omen of the Ancient the first book, Plight of the Gods the second, and The Planet of Whispering Strife the third. Though I originally wrote it so that the events would not need to be in exact sequence, this would improve the introduction of a few key characters and plot points. Essentially, the intro book to the series would not be bombarding the reader with new concepts so early on, and important details in Final Exodus would be more likely to be picked up when transitioning straight from The World of Whispering Strife. The main barrier to this is making sure enough from Omen of the Ancient is understandable and interesting when it becomes the starting point for those new to the series.
Another important update has also been made, being the fact that I'm now about two chapters away from completing the expedition arc in Plight of the Gods. Right now, there are about ten new chapters all lined up together that I built from two or three shorter ones that only summarized the events that transpired (and not in a good way). Once the arc is complete, there are about three more chapters to complete in different spots of the book, and then that too will be ready for the beta reading phase. Plight of the Gods is now the longest book, currently sitting at 81k words, and likely going to 85k. That being said, the future changes to The World of Whispering Strife are so extensive that it might surpass that. For instance, I've written parts of a whole new character arc for Talmanus, ending his quest for the fountain of knowledge while simultaneously sharing key information about the Surveyor (eliminating a really crappy chapter that just has the Surveyor giving a monologue for no good reason). This new change had me so excited that I basically wrote the whole conclusion on a whim. When the writing happens so easily like that, you know it's a good sign.