Greetings.
Well, to answer your first question concerning whether practicing scales will help with arpeggios, they shouldn't. Practicing scales is practicing scales; and practicing arpeggios is practicing arpeggios. Each use different hand movements and each serves a different purpose in playing. Make sure to also practice arpeggios as they are often found in literature. I don't entirely undestand about what you mean by "fingers pulling away from each other," but assume that you mean stretching. Concerning broken arpeggios, it is important to use the wrist as in grabbing the notes. I hope this makes sense. I use the twisting motion, as in the wrist twists. By "rest on the keys" do you mean that your fourth finger wants to play the note? The fingers should at all time be relaxed and not held in the air in tension. This could mean that whilst the other fingers are playing chords the resting fingers are just lying on the keys without playing them. I hope I made some sense.