DH and I did an end to end tour of the Katy in September of 2011. We used a tour company called Independent Tourist that moved our luggage from point to point. They also made all of our B&B/hotel reservations.
At the risk of offending anyone who really loves the Katy, my husband and I were pretty underwhelmed. The trail itself is nice. I wouldn't call it the most scenic area I've ever seen, but it was fine. It's mostly flat, although the section from Sedalia to Booneville has a bit of a grade. You'll feel it, especially if you're towing something. There are long stretches of the trail where there aren't a lot of services. The trail runs through some pretty depressed areas, and I found it more than a little unsettling and sad. We stayed in some towns where there were few places to eat, especially if you arrived--as we did--on the day that a lot of places are closed (Sundays in Sedalia and Mondays in Rocheport). We were sometimes lucky to find any food. Healthy food generally wasn't even an option. We did like Hermann and Saint Charles, and we loved our B&B in Rocheport.
I'll be honest that I think the upper end of your mileage goal is overly ambitious. We rode 40ish miles a day and that was more than enough--and we weren't loaded or towing anything. Granted, we did it in September and had less light to work with, but I wouldn't have wanted to ride much more each day, even with more light. It just felt slow going at times. If we'd had to battle summer heat, I think we would have been even slower.
I say all of this knowing that a lot of people have done the Katy and loved it. You and your kids may have a completely different take on it.
Live with intention. Walk to the edge. Listen hard. Practice wellness. Play with abandon. Laugh. Choose with no regret. Continue to learn. Appreciate your friends. Do what you love. Live as if this is all there is.
--Mary Anne Radmacher