To play organ music, a pedal board is pretty much required. Without a strong bass line, the organ will sound weak. And you can't add 16 foot ranks to the manuals - that produces an awful growling.

There are some alternatives out there. But just a few companies makes pedal boards suited for a huge pipe organ. Depending on which standard you'll shoot for, pedal boards usually has 30 or 32 notes. As far as I know, the european standard is 30 notes, while US standard dictates 32. Personally, I went with 32 notes. I believe that it is better to do it now, than to be sorry later for not having the full compass.

I am going to build a three-manual stack of keyboards. I've bought three M-Audio Keystation 61 ES, which is a very good alternative for organ manuals/keyboards. The weight and touch of the keys are very close to a tracker organ, even though you won't get the little "edge of resistance" that exists in tracker organ.