I am sorry that your questions have not been asnwered. Our other ISEF Experts have not been available lately. I do not usually monitor this forum, but I have been to ISEF before (2007) so I will now be an Expert for this forum and answer your questions as best as I can.
1.) Excellent--I wanted to go back, but I was a senior so I only got to go once. It is definitely a nerd fest, and an international one at that--there are people from Asia, Europe, etc. all talking about sciences of various types, new theories, and such, but everyone is so similar that you get along really well and find yourself adding to the nerdy conversations. It's not awkward or bizarre just because people are well-educated--on the contrary, it is a heavily social event, and a wonderful experience. Plus, it is very exciting to present your projects to the public and to judges. I loved going to ISEF, and I'm excited for you that you get to go too!
2.) The only way to anticipate tough quesitons is to practice before you go to ISEF with someone who really knows what your project is. Let's say you did something in physics. Get a physics teacher at your school (AP physics teacher if you have one), or perhaps a physics teacher at a local community college, to quiz you and test your knowledge of your subject matter. The only way to prepare is to be asked tough questions before you go, so find someone who is qualified to do so and do it. That's what I did, and it really helped out.
3.) If you can make it look nicer, go for it. It's not about the board, but there will be people there with very impressive set-ups, so you don't want to fade into the background. Don't rely on the board too much, but definitely improve how it looks in some way. Make it big, easy to read, and have a nice color scheme which attracts attention but isn't so flashy and gaudy that it turns people away. Your board advertises your project so that people will want to come and check you out and ask you questions and learn something. Try to make it exciting but keep it sophisticated. Does that make sense?
4.) Definitely wear business formal--suits and ties for guys, dressy business outfits for women. Imagine yourself working at a large corporation--what would a CEO wear? What would a secretary wear? You want to dress to impress.
5.) Besides presenting to judges, special judges, and the public, you will also be going to two awards ceremonies (normal and special), and a welcoming ceremony. Plus, there is a lot of downtime for you to spend time with people, explore Reno, do some shopping, etc. On my down time, I explored Albuquerque, New Mexico by having dinner with friends, meeting new people, and hitting some science museums. There is also a scheduled social event with food, dancing, and music. Plus, in my case, I was given one fully-paid tour opportunity, so we had our choice of any number of local tours to go on for free! My choices ranged from a railcar which takes you high above the New Mexico mountains, the Trinity Site where the first atomic bombs were tested, the Intel headquarters, the open desert where there was a lot of native history, etc. I don't know if you will have all the same things since your ISEF coordinator may be different than mine was, but trust me, there will be plenty of social events, lots of recreational down-time, and many opportunities to make friends. Oh, and I almost forgot, on the first night there is a pin exchange--make sure to bring several souvanir pins from wherever you are from, because on that night you will be trading pins with everyone who is already there. You could end up with hundreds of pins, so plan accordingly for bringing some to trade, and bringing them back with you. I came home with tons of pins from other states, but also from Japan, South Korea, European nations, Israel, Turkey, etc. It's very exciting, it's a great ice-breaker, and you meet so many amazing people that you don't want to miss that event!
6.) Make sure that you DEFINITELY have a backup plan for everything. When I went, the airlines I took lost my poster. Luckily, I had brought a flashdrive with the poster on it, so I went to a graphics store and had a new one printed in time for me to display it at the fair. Make sure you prepare as much as you can before you go (like I said about "tough questions"--really know your stuff. Be prepared to talk to little kids--there are lots of local schools which take a field trip to the ISEF to talk to you, so be prepared to explain your project for all different comprehension levels. Take lots of pictures--this event will be amazing and you will remember it for the rest of your life, so be prepared to capture as much of it as you can, because it is over too soon. Meet as many new people as you can, and get their contact information (Facebook, Myspace, whatever) because you will definitely want to stay in touch with lots of them, and you may even want to track them to see if you'll see each other again at the next ISEF (assuming you both can go again; I wasn't able to because I was a senior in high school so it was my final year to be able to go). Again, definitely dress to impress. Be adventurous and explore--don't waste your downtime. Make the most of this opportunity, becuase it is very rare. And finally, really really get something out of the scientific end of this event--learn from others, explore other projects, ask questions--remember, it is a science fair primarily, so don't make it ALL about socializing. There is a lot of amazing science out there, and some people have brilliant ideas, so broaden your horizens while you have the opportunity. Above all, enjoy the event, take it all in, and make the most of it.
I hope I've helped. Feel free to ask other questions!
O God, Thy sea is so great, and my boat is so small!