2) This is more global advice, but I haven't exchanged money in the US in advance of a trip in a very long time. Just hit an ATM once you land. Find a bank that refunds ATM fees and make sure you have a 4 digit PIN (longer ones sometimes don't work overseas). I carry some USD for an emergency but never use it. If you do have to exchange, do it locally, not in the US - rates will almost certainly be better abroad.

3) Taxis are very cheap and very plentiful. Just be prepared to give the destination in Chinese. Finding it on your phone and showing the driver works.

4) T-Mobile has free data roaming nearly worldwide. It's slow but works for maps and email when there's no wifi.