I'll start off with some general answers, and then perhaps someone who knows more can add more detail.
I've played a few reed organs, but certainly don't feel I'm any kind of expert on the subject. I did, at one time, think "reed organ" and "harmonium" were the same until a friend told me emphatically that they are different. He didn't go into details, though, so I can't tell you how they're different. I would guess that often when people say "pump organ" they mean "reed organ," however there are pipe organs that are pumped by hand.
The stops on the reed organs I have played have names like pipe organ stops, except the sounds are produced by reeds. These instruments do not have pipes, only reeds, though I guess perhaps there could have been some kind of a combination instrument made along the way sometime. . .But in general, it refers to organs with no pipes.
Voicing of organ pipes is a very complex topic, and it involves a lot of experience, knowledge, and even intuition. I am nowhere near an expert on this subject, though I have worked with one voicer in particular who now works for the Fisk company. I believe that voicing involves many things, such as opening or closing the toe hole, adjusting the languid, adjusting both the lower and upper lips, and perhaps cutting nicks on the languid. A good voicer develops an intuitive sense for what needs to be done to get the attack right, get the volume right, get the tone right. . . What I did was sit at the organ console, holding notes, and listening and giving feedback as to what I perceived the tone needed. The sound, of course, is different out in the room than it is right next to the pipes.
Perhaps someone who knows more on these subjects could give us more detail or correct errors I might have made. Otherwise, if you still have questions, ask away and we'll see if we can help some.
Tom Dressler