Packet pickup and Expo: This is a huge event and is held at the convention center. The parking isn't an issue with the parking garages as long as your prepared to pay $15-$20 depending on how far your willing to walk. The expo is huge with just about every major vendor present some with great sales taking place at the expo.

Race Day:
Again parking can be an issue so carpooling is recommended. Once you arrive to the starting area (Expo location) they have an indoor area with a bag drop by race number as well as bathrooms. This is the same place you will return to after the race to get your bag back, get your food and meet with family.
As it gets close to race time everyone will head outside to get lined up in the corals. These are done by letter and will also have bathrooms available. One thing about this race is that it is probably the best supported race I've been to with aid stations and bathrooms located throughout the course.
The coral entrance is controlled by volunteers and race officials to make sure that a D coral runner doesn't go to A or B. They want everyone to be running with the right speed group so you don't end up behind someone doing 30on/30 off when you started your race with the 4 hour pace group or faster.
The course is mostly flat with the exception of some interstate underpasses were you will go down and then back up to street level. The course will take you from downtown through Rice University, through the Galleria shopping district and north through Memorial Park. As you approach the end of the race you will go back into downtown and don't be surprised if your GPS gets a little off from the large buildings.

When you finish you are directed back into the convention center area to pick up your drop back and get food and medical as needed. You are then able to meet with family in the family meetup area with letters designating meetup spots.

For spectators: There are many places in all the major areas of downtown Houston to watch the race and many cheer from multiple locations. At the finish there is a bridge they build just after the finish line for people to cross the course so that they can meet up with their runners and if you have a stroller or wheel their they have a gate with volunteers who will look for a safe time to cross the line of people coming from the finish line and entering the convention center.