Thanks ray! looks like the best option for me would be to get to the chain of rocks bridge.
You definitely have to go at least to St. Charles and Frontier Park on your Lewis and Clark expedition. The Bike Stop Cafe - right across the street from the park - is a great place for coffee, food, water, and any bike repairs or parts. They can also give advice on routes in and around St. Louis.
The route I outlined actually backtracks a short way to take advantage of a dedicated bike trail that runs through Creve Coeur Park.
If you want to ride through the city, you can of course, pick up route 66 in St. Louis. The route linked below gets you to the Illinois section by way of some of route 66 to the Arch and the River Front trail. As the Arch commemorates the Lewis and Clark expedition and is on the official ACA route 66 map - not a bad transition between routes. I've done the Nettles connections as well. They work well and I like their simplicity. Time is about the same but complexity, traffic, and scenery differ greatly - options to match your mood.
(You might take also look at the ACA route 66 map to see how they get folks efficiently through St. Louis. A simpler route than mine.)
(Have fun with the planning; you know it will change once on the road.)
https://goo.gl/maps/3aZsPPWuHSv8va158