David W. answered 12/31/19
PhD in Music Composition with 5+ Years of Teaching Experience
The soundfont will give you a rough idea of how the music will sound sung by an actual chorus, but, as you note, among many other differences, the lyrics are missing. Balances between parts will be off. There will be none of the subtle variations in tone color with register that an actual chorus can produce.
The only solution to this is to listen to a lot of choral music, so that you can fill in *in your head* what it will actually sound like. If you can do this live, that's great; if not, recordings can still be helpful. If you can follow along with scores, so much the better. If you can get your chorus to sing partial drafts of your piece, that could be very helpful; how often would depend mostly on what else the chorus was doing and how indulgent the director is toward your project.