Thank you all for your help. I ended up opting to completely start over, in hopes that I end up with a better starting point before having to manually edit. I did a lot more cleaning up on the images themselves (cropping edges, headers, etc), and used ABBYY FineReader for OCR + .epub conversion this time (instead of Acrobat + Calibre). Now, the resulting .epub was clean, (relatively) concise, quick to load, under 1MB, and most importantly, opened up just fine on my ereader.
I'm a bit embarrassed to have uploaded what seems to be the worst formatted .epub ever seen (

), but I'm happy to have learned from it and hopefully I know enough now not to make the same mistakes twice.
Thanks again for all your assistance and guidance! Now I'm off to finally enjoy my book