After surgey when should you start doing exercises, and what kind? Are the toning band exercises good to prevent loose/sagging skin? If not which exercises are good for it?

Most docs seem to recommend 3-6 weeks after. I'd say that the important things is when you're no longer getting pain - there's no point rushing to exercise and giving yourself an injury. Walking is permitted off the bat so get started with that and build up gradually from there.