1. That's just up to you. You don't have to get into any major details. This question is really just to break the ice a bit, and get the conversation rolling. There's very little you could say here that would make or break the job for you.
2. Since you have no prior work experience this question probably won't come up if the hiring manager is paying attention. If the question comes up about your lack of work history, just tell him/her that you've mainly been concentrating on school up to this point, and now that you're out, you are looking for something to which you can apply your attention and efforts. You're not looking necessarily to make money. You're looking to work.
3. If you truly don't know what you want to do for a career, then tell them that you're fascinated by the possibility of a career in the restaurant industry, and that you feel an entry level position, such as a busboy, will be the first step of gradually learning what it takes to run a successful establishment. It'll also help you appreciate every aspect of the operation when you're managing your own restaurant some day. This may seem like overly exaggerating your enthusiasm, but how do you know for sure? You might end up loving the job, and find that you do indeed want to pursue a career in the industry.
A lot of interviews will include questions about how you deal with certain situations, in hopes of determining how you handle stress, conflict, ethical issues, etc. Always side with honesty. If they are asking how you'd react in a scenario where your friend/coworker is stealing supplies or doing something else that's wrong, you always take the honorable approach and inform a manager. In fact, almost any question that involves a situation that affects the company should be answered with whatever is best for the company. You might lose someone who you thought was a friend or the respect of a coworker, but he/she is not the one signing your check, right?
Prepare yourself by collecting some of the stuff I've shared - Also, google other great typical interview answers - and develop a list of open-ended responses...the kind of stuff that could be an answer to almost any question.
Now recite these responses in front of a mirror. It's important and very helpful to record yourself giving the answers, so that you can go back and listen and determine where you can make things sound smoother. You will want to record your voice so that you can spend the time in the mirror watching yourself rather than listening to the words. Watch your body language and make sure you always keep a decent amount of eye contact. When the hiring manager is talking you should always maintain eye contact to assure him/her that you are paying attention.
Interviewing for a first job is an unnerving experience, but practice will help you be a little more confident since you already have an idea of what you want to say, and then you're just putting your concentration into adjusting your pre-developed answers to fit the questions. The person interviewing you knows you're nervous, so don't be worried about that. I've been nervous for every interview I've ever had, and that's WITH practice. I'm sure most people would tell you the same thing. With that said, do your best to show confidence in yourself and it'll go a long way with the manager. You want this job, right? Well, prove it to him/her, and walk out of the room leaving that person with zero doubt that you're the best person for the job.
Hopefully that helps.
Good Luck.