I would say no sash too!! I love the lace and the detail it has of fading down and I feel like the sash would take away from that. I wanted bling but have an all lace gown and it took away from It. If you are doing a veil or hair comb and want bling maybe add it there? I love your dress!
As a fellow short waisted Bride, I vote for the belt. It will define your "waist" and make it look smaller. I'm definitely wearing a belt, for the exact same reasonI would opt for the wider belt, instead of a smaller one.Congratulations!❤
To your question, I personally absolutely love the dress without the belt. I think adding the sash would distract from the elegant patterns. Your dress doesn't seem to have anything sequin-y or glimmery on it, so it might look a little out of place, too.
Just one opinion. But boy, I do adore your dress and veil. You are going to be a stunning bride!