I usually do a water change before adding in meds just to be on the safe side. For extra course, I mean the 1-3 doses every other day for another 3 doses. With dropsy symptoms, if you are not absolutely sure you've treated thoroughly, the bacteria can strike again and be more resistant and hard to treat. When dosed this way, Kanaplex is safe for another course.
If he seems to be doing okay without the epsom salt, you can always skip it but it won't hurt him to have it in there. You can start him out on 1 tsp a gallon and if he seems okay on that, leave him at that level. Otherwise, work him back up to 3 tsps/gallon again.