Hi there,
thanks for the kind words!
Regarding your questions, yes installing the Zaquencer firmware meakse the BCR become exclusively a sequencer and removes all original controller functionality.
You can re-install the original firmware to make it work as a controller again, but this will get rid of the flash content (controller mappings/sequences) in both directions, and it will either have to be restored via SysEx dump, or by reprogramming.
The 4 tracks, or sequencers as you call it, can be freely assigned to a Midi channel. Even drums are not fixed to 10 (but can be of course), and can be assigned any Midi channel.
Yes the BCR can still be used with an iPad after installing the Zaquencer, but as a sequencer of course. Also bear in mind that installing the Zaquencer gets rid of the USB function of the BCR, so you need a Midi USB interface that works with the iPad.