Please use a respirator while you sand. You will have a huge load of dust from a power sander.
Unless you have large ridges to sand down, I would not recommend a power sander at all because of the dust. A little trick my son taught me is to use a spray bottle of water, spray the ridges, let it soak a little and scrape the ridge off rather than sand. It eliminates all the dust. You could then apply another thin coat with a wider trowell trying to eliminate all the ridges, maybe even use a third coat if needed.