Right, I'd cut the collar off to get a smooth elegant line. Then you could edge it in contrasting bias, or ribbon, even a black ribbon would be nice and quite classy.
If you shortened the belt, could you then wear the dress with a contrasting belt over the top? Either a wide leather one or a nice fabric one. An obi one would be nice and tutorials online for this.
I really like that necklace. You could make an extra flower to attach to a bag, or wear in your hair, or on the belt.
Team with opaque tights - I tend to go black as legs ok but not best feature - although bright coloured opaques are very trendy now. Maybe coordinating with corsage or doing a trendy clashing thing.