I created a choir arrangement for the old song. I sang it all by myself - three tracks each for each voice, 12 total. The soprano tracks are one octave too low, the times that I could sing soprano are long gone. 
Piano by Qsynth plugin, organ by SetBFree, Reverb IR with the impulse response created by my program I mentioned earlier. I really should publish it some nice day…
I used Musescore for the score and transferred the midi export to Ardour to have reference tracks for the remaining work. The piano and organ tracks were played via Masterkeyboard into midi tracks. They are kept rather simple to leave room for the voice tracks.
