I have done the entire length of the KATY trail twice. Once was from Clinton to St Louis. The Other was the other way. Each time, I had a group of about 20 to 30 people with me.
The hard part is negotiating the transportation issue. It is point a to point b, unless you ride all the way out and back. The train is an option unless you have a recumbent or tandem. They also do not take trailers or panniers.
Like someone else said, pay heed to the weather. A wet KATY trail is a miserable KATY trail, particularly in areas they might have recently dumped some chat.
This site here:
http://www.bikekatytrail.com/ was a big help to me.