Ann Arbor is an intermediate stop on the three-times daily Chicago to Detroit service, one of the relatively few such 'frequent' operations in the USA. It's broadly like a UK train, get there on time, follow the signs, etc. If you don't visit Chicago Union station beforehand then do allow time to explore it and take photos as described above. Like many major US stations the classic building is a real interest; the tracks where the trains are is a rough and gloomy industrial add-on in comparison, and can't be accessed until your train is ready.
The initial departure from Chicago has a lot of rail interest on both sides from the still significant number of US rail companies that serve and interchange there, so have your camera ready at the window. The scene can look familiar, but it is surprising just how many technical rail terms are different there.
Ann Arbor station, in comparison, is a roadside stop in a smallish Midwestern town, dominated by the large university, whose students make up a significant proportion of Amtrak's passengers there. Compared to other equivalent Michigan cities, a number of which which have lost their car manufacturing plants over the last generation, it's better than those, although I've never got out there, only passed through. Like other such intermediate stations, Amtrak will tell you to arrive at least 30 minutes before train time, which as you can just walk onto the length of the platform from the adjacent street is more than a little silly.
Conventional taxis have pretty much disappeared in the USA outside the largest cities. Uber is there, just check your App works. If you don't tip the driver AT LEAST 20% on top of the fare expect a face-to-face hassle!
USA still uses notes for USD 1, and coins have limited use nowadays.