Oh I do not like that last arch with the fake columns... Im with your mom on this one! But I love your setting, it is gorgeous. You should only do a few points of interest, otherwise all your "decorations" will be competing and it wont be elegant. I think the aisle balls, and the horse & carriage is just right.
If you absolutely must have an arch, make it be wood with a few flowers just at the top, something very simple.