1. You should not have to pay an agent any upfront money to represent you. Agents will get paid 10-20% of your check when you are booked on jobs. Agents get paid when you get paid; don't get sucked into paying anything upfront.
2. A model book is like an album and each page should have different photos. One could be a headshot, one could be you as a doctor in a full body shot, the next could be a 3/4 shot. The more different the photos, the more diversity you can show the booking agent. And please, don't use one photographer for all of the photos; again, agents like to see variety. Take your time to develop your book.
3. You will need training. People don't just become major actors or models overnight. Or think of it this way: you'll be much closer to a 'yes' with training than you would be without. Find a local reputable school OR program. You can even get experience in your local community theatre or take classes at your local community college. An experienced and trained professional is always more likely to get the job than a novice...just like if you were getting any other job.
4. Aim for non-exclusive contracts. Exclusivity will lock you into one agent; why would you want to be locked in to depending on ONE person when you are just getting started? More agents = more opportunities! And no, you don't need a professional manager until you have so much work coming in that you cannot balance it yourself (or mom/dad). Each person you hire (an agent, a manager etc) means more money coming out of your checks!
5. Check local casting agencies and websites for possible jobs. Start at Project Casting to get a good idea or your local film office! Note: just like there are reputable and non-reputable pageants, there are reputable and non-reputable companies to work with. Don't necessarily jump on the first thing you see on Craigslist! Check out each company BEFORE accepting a job.
I was in the modeling and acting world for over a decade before becoming a Director of Education at a leading modeling and acting school for 5 years; if you have any questions, just ask!