1. Correct.
2. Correct, but you could also say "Cad é a cheannaigh tú?" or "Céard a cheannaigh tú?"
3. Correct, but you could also use "cá" ("cár" in the past tense) instead of "cén áit": Cár cheannaigh tú an leabhar seo?
4. Correct, but "cathain" isn't used everywhere. "Cá huair" or "Cén uair" are alternatives.
5. Correct, but there are also other ways of asking "why?", such as "Cad chuige?", "Cad ina thaobh?"
6. Correct, but you could also use "Cé acu leabhar?", especially when it's a choice between several specific books. This phrase is also useful for asking things like: Cé acu leabhar nó iris a cheannaigh tú? = Which did you buy, a book or a magazine?
7. "Cá mhéad?" or "Cé mhéad?" (followed by the nominative singular) is the correct way to ask "How many?": Cé mhéad leabhar a cheannaigh tú?
8. & 9. "Cén cineál?", "Cén sórt?", "Cén saghas?" are all followed by the genitive singular, to express "what kind/sort OF book, etc.".