Roy: As a fan of the early work of Don Imus (read prior to 1974), one of his characters was the Right Rev Dr Billy Sol Haggis who sold a Bible with every page blank....
Its great that you are starting to experiment with BookDesigner. It is a powerful program that creates great books. There is also a program by Kovid Goyal called html2lrf that is adding features on an almost daily basis. I have played around with it but I am still more comfortable with BD.
For sources of
Progress I used
www.gutenberg.org. They are great and everything there is copyright free in the USA.
Now for something quick and dirty that I will never read again or something that I don't (or can't) share, RTF files are not bad. They will scale font sizes just like LRF files but they do not have graphics (on the Sony Reader), they have no chapter breaks, and there is not a Table of Contents. For a short story they are not bad, for a novel they are acceptable (sort of.) For a collection like Harry puts out or your proposed one year Bible, LRF is the best way to go.
Now the same book in RTF and LRF (via BD) will be significantly smaller in LRF as it is a compressed format and there are a lot of format tags in an RTF document. The Reader does a lot of compression when it loads an RTF file so the file size reported in Windows is more than the space occupied in the Reader (if loaded under the Connect software.)
I look forward to seeing books by you in the Reader Upload section.