Cmd chord passes through, so Cmd+Enter still runs the query. Vim and Emacs exclude each other: choosing one turns the other off.
Move the cursor
Kill and yank
Kills in a row join into one entry: three
Ctrl+K presses yank back as three lines. A move or an edit in between starts a new entry. Delete and Forward Delete never touch the kill ring.
The kill ring holds 120 entries and is separate from the clipboard, so Cmd+C, Cmd+X and Cmd+V keep working as usual.
Mark and region
The region shows as the selection. A click,
Shift with an arrow key, or typing drops it, and typing over it replaces it. Ctrl+K, Option+D and Ctrl+Y drop it and act at the cursor.
When more than one input source is enabled, macOS takes Ctrl+Space to switch between them. Use Ctrl+@, or turn that shortcut off in System Settings > Keyboard > Keyboard Shortcuts > Input Sources.
Completions
Ctrl+Space sets the mark in Emacs mode, so open completions with Escape or Option+Escape.
Other keys
Option types its usual character on every key the tables leave out. Ctrl+D, Ctrl+T, Ctrl+O, Ctrl+V and the other text keys every Mac text field answers keep their macOS meaning.