Hi friend. When designing your sprites try to draw them always facing right.
Use the rotate to direction can work pretty well with the set mirrored function depending on what you want to do, since you're only playing with construct 2 there are a bunch of cool stuff you can learn from those functions, just look for some tutorials here in the site.
And yes, you can change your sprites and animations after developing the entire game. Usually when I'm starting a new project a use only squares, circles and other simple shapes and the actual design and animation I add at the last part of the game along with the music.