Best way to make a well-formatted omnibus book?
I want to make an omnibus ebook of the Twins series by Lucy Fitch Perkins. Gutenberg has the first twelve books and I want to read them, so I thought it would be a good first project for me to make an ebook I can contribute to the community. I am unsure of the best way to proceed though given that some of the books have different formatting and styles. Some have illustrations and some do not. Some indent paragraphs and some do not.
I also want to have a table of contents for the whole volume, and then for each book to have its own too. This is a wish and not a need since the books are short enough that I suppose it doesn't matter much. But if it's easy to do, I feel I should.
So, how do I work with these books given the formatting issues? I was thinking I would use the Gutenberg HTML, cut and paste into Open Office to get plan text, and then paste into a Sigil file. Is there a better way?
Also, for the table of contents issue, i know how to use the headers in Sigil to generate a TOC but I am not sure how to do a sub-toc so each book has its own. Is it better to do each book one by one in Sigil the regular way and then use the merge ePub plug-in from Calibre to make the omnibus?
Also, does anybody have any suggestions for a website or free Mac app I could use to easily make some simple covers? I just want to be able to choose an image and then have text above and below it for title and author. Maybe when I am done I could find a volunteer here to do a nicer cover for the whole omnibus.
This will be my first contribution to the library, although I have used Sigil a little before to correct my bought ebooks. I hope others will enjoy the book when it is done and I welcome any suggestions for best way to proceed.