1. It is loud - They play music throughout the run, some live and some not. Gabriel either enjoys it or completely shuts down.
2. It is Very Crowded - they had over 11,000 registered runners not to mention spectators. Again this could go very well or be a complete disaster. Gabriel could shut down or even run off.
3. The color - With a sensory kiddo you are never quite sure how something new like people throwing powdered color on you might end up.
Overall things went better than I expected. Gabriel refused to walk due to being extremely over stimulated so I carried him on my back. With this simple (and heavy) adjustment he was able to enjoy the 5k.