There is no easy way to create an ePub for a book such as yours with tables and many pictures. Images but especially tables and the like need special consideration. Some new learning is needed and time needs to be invested into learning the structures and limitations of ePubs.
A good tool to learn to use is Sigil.
But you won’t learn it overnight, if you can design good web sites and understand HTML and CSS then you stand a good chance of doing so.
As your print copies run into several hundred pages you may like to consider creating an ePub Box Set where you take each chapter in turn with its own ePub. Put all your effort into creating the first one and later conversions should be easier. What you should be concentrating on is creating the ePub as an ePub not just waving a wand to convert the existing print version.
It’s also worth considering learning to use InDesign to create professional print books (it has a great and simple print to ePub converter).
Try browsing some of these publishdrive.zendesk.com/hc/en-us/articles/115003164394-The-epub-format-advantages-and-limitations www.theheratik.net/books/tech-epub/chapter-7/ kb.daisy.org/publishing/docs/html/tables.html yourscriptdoctor.com/tables-for-indesign-epub-export/
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