Hi, Maybe I could give a little tips for you.

1a&b) Golden Triangle - Too busy, traffic heavy n surrounded by shopping mall. Easy xs to food.
c) China Town - Interesting food & cheap, Traffic heavy, Cheap hotels . Business hour start only at 6pm onwards.

*1.Accomodation, You might want to try Sheraton Imperial - Easy xs to many interesting entertainment club. walking distance to HardRockCafe, Food Ctr etc.
tips.. 1.You do not need to worry abt transportation coz there is lots of mode of transport everywhere in KL eg: monorail, LRT, Taxi, City buses.
.......2.Trip to KL will not complete if you didn't visit the National Museum, Istana Budaya,KLCC tower or KL Tower, National Mosque, Dataran Merdeka n Batu Caves.

2) 3 wks I guess..??

3) a)Langkawi Island (by train from KL) - Beautiful Sea, Nice Resort (Bonton),Nice seafood, water sport etc
b) Penang (by ferry from Langkawi) - Busy city, Cheap & tremendeous selection of food (U'll love it!) lively nitelife, good,good,good. Recommended htl - Eastern & Oriental Hotel (five star*)

c) Sabah (by flight - air asia is cheaper) - Good & cheap food, nice forest & mountain, Place for you to just chill out n total relaxation. Try to stay at the Datai or Andaman.

Anyhow, more info in this website : http://allmalaysia.info/

Hope this will help.