1. Will Call. If it's the same as all the other years, Will Call will be in the Wabash East Concourse hall way, on the bottom left of the convention center map. On Wednesday, the line has been about 30 ish minutes, depending on the time of day. I've never waited through the line on Thursday, but I've heard that it could be over an hour. I'd recommend getting your stuff mailed if you can, it's been accurate all the times we've gotten them shipped. Attendance is expected to increase this year for the 50th so the lines will probably be longer.
2. Entrances. All public doors into the ICC are open 24 hours a day for people entering and exiting. There are no lines or check in/security to go through in order to enter the convention. I know there are LOTS of entrances along the bottom and left side (looking at the official map) of the ICC. I've never used any doors on along the top or right sides and I'm not sure they are accessible. There will be a swarm of people waiting in a mob outside the Exhbit hall doors (Inside the ICC) for when they open at 10:00AM. Those people are wanting to rush in to get limited goodies/games. Unless you are wanting something limited, or just want the experience, I'd suggest you avoid that rush. I've never done it, so I'm not sure what time people start camping out, but it's probably at least an hour before 10AM.
3. Your badge will get you a swag bag, which you can pick up in the Wabash East Concourse, It will have a event catalog that will also have a map of the convention, showing where different gaming groups are running their events. The catalog itself is quite heavy, so i'd suggest just taking a picture of the map and leaving the catalog behind if you are in for a long day. As for actual signage throughout the convention, I've found it to be quite adequate. There are large stickers on the carpet with arrows to different near by gaming rooms and the hall letters are marked with large signs. Other GenCon attendees are pretty helpful, and a lot of them have been coming for quite a while, so asking someone passing by for directions is always an option.
4. The 1st floor hall ways are quite wide and I've never found them to be congested (except for outside the exhibit hall doors before they open at 10AM), so going up to the second floor to shave off some travel time is pointless.
5. The exhibit hall is probably the most noisy congested, information overload area of the convention. The second floor tenders to be a bit less busy, and the smaller gaming rooms up there tend to be pretty chill, unless there is a particularly routy event going on. Every year there has been a "quite room" for people to go into if they just need to relax and take a break from all the noise and congestion, I remember that being some where on the second floor.
6. Food. There is convention food, which is sold in various vendors throughout the con. It's expensive and not that good. They say that you aren't allowed to bring any outside food or drinks, but in the 8 years that I've gone, I've brought about 2 meals with me every day, and never been, or see any one else given any resistance to them bringing in food. To the left of the convention center, in between S Capitol Ave and S Illinois St there is a side street with that grey strip down the middle of it. There are probably about 20 food trucks lined up along that street every day, so you could pop outside the convention and grab something to eat from one of them. There are also many good places within walking distance if you want to get a sit down meal, I specifically recommend the Spaghetti Factory, we eat Wednesday dinner there every year. There is also a Stake and Shake just down W Maryland St. A burger and shake tastes pretty good after a long day walking around the convention. It is usually pretty packed though, even at 1 in the morning. The various down town pubs are pretty packed throughout the con.
Hope that answers your questions!