I've listened to it all and it was interesting to understand how it works in a catholic Dutch church. Pretty long improvisations in there. Must be tricky to keep on going that long.
Yes it is tricky as you must be prepared to stop at any moment and yet don't want to have to break it oiff too abruptly. So I just keep rehashing one or two motifs with harmonic variations. Probably gets boring after a while but that is their problem
To the spring, I will probably play with the children choir which Alva (my daughter) sings in. Not sure if I look forward to it as they are from 7 to 10 years old. But I will use the piano only. I do not dare to enter the organ
Make sure you record it for us !
I'll bet you will get to that organ eventually...