As other said:
- No need to carry passport
- No problem paying with credit card at most malls, but some small shops inside might add 2-3% processing fee
- HSBC in the airport and in the city does not charge for cash withdrawals. Local CIMB does not charge as well
- With street food you will need cash, but not much. Average street food meal would not cost more than RM10, that $2.5. If if you take equivalent of USD $20, it would be more than enough to eat out for several days
- Use Grab for getting from place to place - download and install app and add your credit card, you won't need cash. DO NOT use local taxis.
- Fastest way to get to/from the KUL is via KLIA express, especially during traffic.