I think that you're all in for a real treat!
Here's a few tips to help get you started:
Food on the train can be a little pricey, so I would recommend taking a very small cooler with sandwiches and snacks. You can consume a private stock of food at your seats, but not in the lounge car or in the dining car. Keep in mind the maximum carry-on luggage is two pieces for passenger (not including purses or laptops).
Since you're leaving at pre-dawn and riding for 12 hours, you may wish to bring a lightweight blanket to get some rest. The Texas Eagle has pillows.
To find a seat on the train, look for one that is both unoccupied and does not have a seat check (small stub of paper with a 3-letter code) hanging above it.
I sometimes bring a small bag with soap, wash cloth, toothbursh, etc., to freshen up in the restroom toward the end of the trip.
You may also bring cards, magazines, games, etc. to make the trip more fun, especially when you're traveling with a group.
Hang out some in the lounge car and meet people. There should be some nice scenery, especially as you approach the Mississippi River.
Keep in mind that the trains run late due to various circumstances. Don't get in too big a hurry.
The train platforms at Chicago can be a bit noisy and chaotic. Once inside the station, you should be able to sort yourselves out, get your luggage situated (using the storage lockers, if you need them), and get where you need to go.
On your return trip, get to the station at least an hour early. I usually don't go down to the boarding area until about 30-minutes before departure.
Train travel can be very relaxing and worry free. I hope you have a great trip!