Can I select multiple frames and edit them at once, select an entire frame layer with Ctrl+A, or import multiple files as an animation layer/frame? (Also I want to do it with GIFs so I don't have to split it up and do it manually)
Selecting multiple cels is currently not possible, but it is a planned feature for a future update. You can import multiple image files (but not gifs for now) as new layer and frames in your existing project by changing the "Import as" option in the window that appears when you are importing an image. You can also import spritesheets this way.