1.) The water will be cold as hell. Hope that it'll be a sunny day because you'll get cold AF.
2.) You shouldn't wear regular shoes. You'll end up breaking your ankles or knees because of slipping on the rocks. You need the ankle support from a stiff pair of boots and you need the grip of a felt/vibram rubber/metal studded sole. I can't believe that the guide won't have boots that you can wear.
3.) For what it's worth, when I do wet wading in the summer I wear my boots and a pair of neoprene gaiters/gravel guards. The setup looks similar to what you can see me wearing here: