I installed Sigil and that's working out nicely. I used it a few years ago when I was using Windows all the time. Haven't used it on Linux until now.
Thanks very much everyone for all your help.
I felt compelled to just say a huge thank you again. I've done my little epub and can read my compiled margin notes on my tablet in a decently done epub format with toc all nicely laid out.
-yayy!! for Calibre and Sigil.