I second the motion on getting what you pay for as far as shoes go. Personally I like Tevas. Make sure you walk every day for at least a month or so before you leave, both to break them in and to get yourself in shape. I walk my dog every day and when I was there in January, I walked circles around both my son and GD.
I took Arid creme antipersperant and rubbed it into my feet every morning, then covered them with Body Glide and never got a blister. Whether you use spray or creme make sure it is antipersperant, not deodorant. I couldn't find the Body Glide locally, so ordered it for like $6.99 off the internet. I also used the Body Glide everywhere else on my body that I might chafe. Before I went to bed every night I rubbed my feet with peppermint lotion. I would carry moleskin and blister bandaids into the parks, just in case, but hopefully you won't need them. Good luck!