Hi !
For me it is very curious than an organist has no organ at home. A virtual organ seems to be the minimum. Of course we can play or compose with any keyboard : piano, harmonium, syntheziser, but to hear what we are going to post or publish, it is better to test the music before with real organ sounds.
Personnaly, I play on a midi piano (without any organ sounds). I can linked it to midi synths or expanders, but I had never the organ registration I needed. Since I have a virtual orgal (in fact many virtuals organs now), I can play and hear exactly as if I were in a church. it is a great pleasure to be able to play or improvise at home on a 3 ou 4 manuals great cathedral organ when your room is only 10 square meters. Of course, I have not a pedal board, but many organ works can be played with only the hands.
PS : when I really need to play with 2 manuals, I can use my old Yahama DX7 as the second manual. But often, I prefer to play only with my midi piano, spliting the keyboard inside the virtual organ.