I wore Nike gel flip flops for 6 days in the park once, older tennis shoes another trip. Those particular flip flops felt like I was walking on clouds. I would recommend them again.
Side note: if you spray your feet with spray deodorant, they won't sweat=no sliding=no friction=no blisters!
Clothing-wise, go comfy, but remember you'll be taking lots of pictures, so keep that in mind. I like skirts/skorts with a fitted (not skin tight, but feminine-cut) tee shirt. A pair of earrings or necklace can pull it all together and make the simplest outfit look stylish.