I'll take your questions in order, but Mods, can we sticky a tailgate info thread so the newcomers can see information without having to ask the same questions?
1) Texans fans show southern hospitality and are welcoming to visiting fans. You may experience some mild taunts, but as long as you are respectful and not obnoxious, you should be fine. I think we have a fairly good reputation overall. Cowboys and Titans fans may disagree.
2) Fans tailgating without going to the game need a tailgating pass. The passes are sold to season tickets holders on a first come first served basis. I did hear from some people who stayed in the lot last week that security was charging $20 to people who stayed in the lot and didn't have a tailgating pass. Not sure if that was legit or security was making some side cash.
3) Parking passes are sold out, but you can find them for sale on ebay or stubhub or nflticket exchange. Yellow, blue, orange and platinum lots are known for their awesome tailgates.