Questions about booking/traveling coach
 

I am doing 2 separate legs using points, one from Chicago to Minn, and then a week later Lees Summit (KC area) to Chicago via St. Louis. I will have one large suitcase and a carry-on. 2 questions:

1. I see there is no checked baggage on a couple of those legs. Is there room for my suitcase and a carry-on in coach?

2. Is there a reason to wait for maybe a better deal or am I better off booking now? Do these trains fill up? I will be using points I think.

Yes. Plenty.

Book today. With extremely rare exceptions, prices on Amtrak only ever go up with time.

1. you'll have more than enough room on both trains.
2. all things being equal, it's likely to be cheaper if you book sooner rather than later, and since point values are now tied to the cost of the fare, there's not a good reason to wait if you're sure you will take the trip.

If "Minn"=Minnesota, then that should be the Empire Builder, which has a baggage car and checked luggage.

Neither the Missouri River Runner from Lee's Summit to St. Louis, nor the Lincoln Service onward to Chicago have baggage cars. In both cases, if there's room, your large bag may end up behind a seat or in a vestibule.

When riding the River Runner, I've never had any problems getting even my very large hardside a spot (although it was sometimes work to get up the stairs). However, I've always ridden in business class.

If you can make the early-morning departure of the Southwest Chief in Kansas City, that might be easier, as it has a baggage car and is a straight shot into Chicago (no connection).