I think that I hardly need tell how enthousiastic I am about Hauptwerk. The ability to play at home some of the most famous organs in the world (Müller, from the Bavo kerk Haarlem amd Schnittger from the St Martini in Groningen) is intoxicating.
And if you midify your practise organ you can have the best of both world. Real live tracker action, some real pipes augmented with Hauptwerk. You can go the realistic route, augmenting your practice organ and make sound as if it really has three or four stops extra. Or do what James and I do: play one of the numerous available sample sets. And of course, you don't really have to choose, you can do both things.
I think it is a step you and Ausra are going to enjoy immensely!