Hi Angelo,
1) My recommendation is somewhere near KL Sentral, the transport hub, the LRT(subway), Monorail, Intercity & Interstate Trains. Landed at the airport, you can take the Express Rail Link(ERL) from the Airport straight to KL Sentral for RM35. There are 2 hotels there Le Meridien and KL Hilton. From there, you can use all the means of public transport to get to all places of interest. U may need a map though.
If you love shopping or want to see the real KL NIght Life, then a hotels in the KLCC or Bukit Bintang Area is idle for you.

2)My feel for no.of days. 2 days.

3)It depends on what interest you. Most visitors won't miss the Petronas Twin Towers, KL Tower, Putrajaya-the new & amazing government administrative city, Batu Caves Temple, etc

Penang? You can get to Penang by Train from KL Sentral to Penang. Or you could take a bus (around 4-5 hours drive). My recommendation, get a hotel near the Feringghi Beach. There are at least 10 hotels along that beach. Places to visit- The Beach of course, the seafood restaurant, the Bukit Bendera, the Snake Temple, the Gurney Drive (night life).

Hope that can assist you. Run a search on whatever places i mentioned above.

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Forever Man Utd Fan!