you should give the bridesmaids a nice white wedge to wear, it would go great with this dress. My wedding is also in August, I'm wearing these ivory flats with rhinestones on them from newyorkdress.com they are called KENNEDY, they are not hard to find on the site. They are flats so you can dance the whole night freely.
A clear sandal. Different in style than your own.
depends on the setting, but August seems hot so try a sparkly sandal or pretty wedges. They're more forgiving as heels hurt and they'll complain.
Silver or white heels would be pretty under that dress, preferably silver glittery ones? like these maybe