I bought one of those blowers that Andy LaTorre wrote about. I haven't
used it yet, but I had planned to use it with a 24-note rank of pipes
that would be voiced to play at very low pressure (around 2 inches).
If one needs more air volume a second blower could be added as they are
quite compact. For the money, it's worth a try.
On an O roll, I don't think any more than two or three pipes are played
at the same time, more like one or two pipes. I think the blower could
handle that if it has the static pressure that Andy mentioned.