Browse the race threads here. There are plenty of reports but they may be old. Things have changed a bit over time.
Some tips:
GET THERE EARLY. I usually get up about 0300 and carry a pre-made bagel with peanut butter and something to drink on the bus.
If you have a long line at Movies don't stress. They do an excellent job with the buses and you will get on one quickly. They try to fill those buses so chances are you will be sitting next to someone. Try to start a conversation and tell them it's your first. Most Disney runners are very friendly. Just be aware they may be very sleepy.
The traffic to the start line will look horrible but don't stress. Disney does a great job getting cars and buses in.
Once off the bus follow the crowds through bag check. There is a stage with a DJ and announcements will be made from there, such as move to your corral. There will probably be characters there for photos.
Big tip: Lines for port-a-potties are shorter in the runners-only corral area. Newbies don't know that. They will also have tables with water. There will be another stage at the start line and big screens for the runners far away. Hosts will be out to entertain, inform, and get you fired up. The start is a lot of fun.
Look at the race map when it is released. Hydration breaks are usually at 1 mile to 1.5 miles. If you don't like port-a-potties, park bathrooms are open. There will be plenty of photo ops on the course with Disney photographers. Many CMs come out early to cheer you on. I love that.
The finish is very organized and the volunteers guide you through it. If you are doing the challenge make sure you get all your bling. Ask a volunteer. They are everywhere. You will pass tables of water and Powerade, runDisney snack boxes and fruit, usually bananas, and there will be photographers with a race background. Then exit through checked bag pick up and head for the bus.
Thank all the volunteers. They are awesome. Is WDW still using volunteers? Hope so.
Mainly, have fun and don't worry about your time.