We apologize that it has taken so long for your question to be answered. Our ISEF experts haven't been available lately. However, I am an Expert and have been to ISEF, so I will monitor this forum now, and answer your questions as best as I can. I went to ISEF in 2007 in Albuquerque, New Mexico, thanks to my project on the most efficient wing design. Okay, so here are my answers:
1.) You will definitely want to wear business formal at the ISEF. When I went, I wore a suit with a tie (you know, dress shoes, slacks, collared button-up shirt, tie, blazer jacket, etc.). You don't really need a blazer jacket, but as long as you're wearing everything else you will be fine. Remember, you want to dress to impress--you'll be speaking with judges, representatives from industry and the military, and the public, so you want to look your best.
2.) Yes, there are lots of younger children who come--many local schools have field trips to the fair, so be prepared to explain your project in simple terms. There will be people of virtually every age there, though, so be prepared to explain your project at varying levels of complexity. You want it to be interesting and cool to kids, but at the same time informative. Practicing really helped me before I went to the fair, so maybe you could try that.
3.) You will have that many abstracts so that you can hand them out to people. As I recall, your judges will already have a copy of your abstract which they will have read before they come to see you (they will be prepared to talk to you), but I may be mistaken. It is definitely not enough for all of the judges in the entire fair to have some, but it will certainly be enough for you to give your judges some, and also hand them out to the public at the open house, and other interested people. Also, when I was there, most of us had a few left over, so we exchanged abstracts with our signatures on them, sort of like an ISEF yearbook. If you have any left over, it may be fun to do that with the friends you make at the fair.
4.) The number of judges who will speak with you will probably be around 8, which is how many I spoke with. You will receive a card with a schedule of when the judges will be by to talk to you, so you'll know in advance how many there are and when they will be visiting you. In addition, there are special interest judges such as those from the military and industries who may or may not want to speak with you. There is a separate judging day for these people, and you may be completely ignored by these people (like I was--they didn't want to talk to virtually anyone in my category), or you may be very popular among those judges. For this day there is no schedule, because they just talk to anyone whose project looks interesting and profitable. If you have a project dealing with alternative energy sources, you will most likely be visited by lots of these judges.
5.) I do not believe I purchased my nametag...you're probably thinking of the registration fee. I had to travel to get to Albuquerque, so to be honest I arrived almost too late to register on the day I got there, so registration was a bit of a rush. However, for me the trip was paid in full by the science fair committee from the local fair I received top honors in, so you may not even have to worry about the registration fee. By the way, in addition to the nametag, you will also receive a medal which you should wear whenever you're presenting on the judging floor. This medal means that you've been to the ISEF before. You receive one for every year you are there, so you might see people with as many as four of these medals on, which is exciting!
6.) No category is easier to win in. Every category is scrutinized equally. However, there are some categories which are easier to win special interest awards in (like I said earlier, the alternative energy projects got their attention almost exclusively), but those judges are unscheduled and unpredictable. Basically, there is no easy way to win at ISEF--everyone is working just as hard to impress the judges. The true measure of if it is easy to impress judges or not is if your project is relatively more informative and sophisticated. If you did more work than others, then you will probably have an easier time, but this has nothing to do with what category you are in. For instance, my project was not very impressive because I did not have sophisticated measurements (they were actually rather crude), whereas someone who did something similar was more impressive because he used a better measurement tool and advanced mathematics to produce better, more relevant results. But there is no way to know if you project is better than others, so really this is also no way to see if it will be easier on you than others. Don't worry about it being easy to win--worry about doing your best in order to try to win. It's not all about winning, but if you can impress the judges and come away with an honor, that means you really did some world-class impressive work.
I hope that my answers have helped. Please feel free to ask anything else of me, I will certainly answer you! You're going to have a great time at ISEF, and want to go back again. I hope you're not a senior in high school like I was, because when it was over I was disappointed that I had not started doing science fairs earlier because I would have loved to go to ISEF more than once.
O God, Thy sea is so great, and my boat is so small!