1. They are both correct, but mean different things. A 'comic' can refer to a thin, unbound publication. Like magazines, comics might come out once a week or once a month are quite cheap and are usually thrown away after use. A 'comic book' is an actual book containing cartoons and comic strip stories.
2. Neither sounds natural. Can you explain what this is?
3. She isn't interested in either ... or...
With positive verbs, you use 'both/and' and with negative verbs you use 'either/or'.