Almost every settle location in the game has access to at least one river tile for a Gristmill and Sawmill (Saw Pit doesn't require a river). Navigable rivers are definitely useful, but are barely any different from coast in that manner. Shawnee are indeed the one exception, but this only applies to navigable rivers.
Thing is, everything rivers do is something that you also get if your city isn't on top of them or adjacent to them, with one exception - the 5 happiness from fresh water. Meanwhile, in Civ VI, the thing rivers gave you was an extra three housing, which was absolutely vital to get a city up and running in a reasonable timeframe (unless you were rich enough to just turn 1 buy a Granary, but that was more of a lategame thing).
In Civ VI, a settlement without a river was gimped (unless it was adjacent to a lake), and one that didn't have an Aqueduct spot was terrible. In Civ VII? You're losing out on some happiness. That's it. Might matter in a crisis if you're also over your settlement cap, but it probably won't.
As for understanding the terrain, it's again quite simple for me. Everything gets settled (unless it's too far away but that only lasts until I settle closer or the AI settles it). If there are good adjacency bonuses, the settlement becomes a city. If there are no good adjacency bonuses, it becomes a town. If it becomes a city, the urban yields are what matters. If it becomes a town, I build fishing boats and farms, and once it takes 10+ turns to grow (which is almost guaranteed to be before it runs out of fishing boats and farms to build), I specialize it.