Easiest and most comfortable is to fly F SQ SIN-KUL and MH KUL-SIN. Saves a few dollars over SIN-KUL-SIN and get the best lounge at each airport. Flight itself is short - can spend almost as long on the ground as in the air.

Depending on where you are staying in KUL as best transport when arrive. If hotel near Sentral then take the express, and either walk to hotel or short cheap cab ride. If further away probably better off taking cab all the way. From the airport its fixed fare based on zones.