I would sign up for multiple FF & hotel programs since there is no cost. Your company policy may dictate which flights / hotels you have to take. We also don't know what the new AA / US merged company will look like. You mentioned a preference for UA, but what will happen once US leaves star alliance? Are you ok with UAs schedule and transferring in UA hubs?
I agree with the Chase Sapphire Preferred as your first card. Some of the hotel chains offer very tempting credit card bonuses, so I would consider them after the Sapphire.