Thanks for the tips, everyone. I definitely think it will be a rewarding hobby---I have experimented already with modifying a reference book I found which had errors in it. I am also thinking of putting together my own poetry compilation of favourite public domain poems.
I do want to standardize across the volumes. I think that since the books are fairly short, I will keep one book per 'file' in the Sigil file and just use heading codes to generate the table of contents. What I am inferring from your comments is that if I make the title of the book TITLE in heading 1 format, and then the chapter title as 'Chapter' in heading 2 format, that will make a nested TOC?
I appreciate the help. Any suggestions for an easy way to make a cover?