1. You're correct about lifting capacity and height. You also have to choose between electric or propane, but keep in mind certain types of forklift are only available in one type of power source(eg: reach type will only be electric). Turning radius may also be a factor depending on your type of warehouse. Can you provide any more detail as to what it will be used for, and duration of use per day/week?
2. Finding an operator shouldn't be difficult. And you can pay to have them certified to operate whatever type of forklift you end up buying, training is done in a couple hour session.