I think it’s a bit more complicated than just the copyright on the written work (particularly if the work is “public domain” because of a Creative Commons license) so it’s best to consult a lawyer. I believe Project Gutenberg does have a page of policies outlining how material can be used and under what conditions attribution is required. Adaptation for personal use is generally far less onerous than adaptation for personal use. But most of your questions can’t be answered without knowing more details about the specific work and what your plans are for the work which is why you’d need to hire yourself a lawyer who can give you a more definitive answer than anyone on the internet can provide.