Finale works the same way, FWIW.
In Dorico, you generally don’t need to enter rests – you just move to where you want notes and enter them, and Dorico supplies the rests for you. This is a conceptual thing that many people have difficulty with at first. Edit: If it helps, the spacebar will advance the caret by the currently selected note duration, so you can think of it as “entering” rests. I use the computer keyboard to enter notes, so if I want to do quarter note, quarter rest, quarter note, that’s just note name, space, note name.
Because the arrow keys by themselves move you up or down a staff. This could have been programmed the other way around; I don’t think one way is intrinsically better than the other.
If you click on a note and hit Delete, you’ll get a rest of the same value.
Without getting into all of the detail about how Dorico uses voices, I"ll note that every voice is created by the user. Note that Shift+V will always create a new voice, while V by itself will switch among existing voices.