I went to Langkawi and Penang on my first visit to Malaysia a few years ago.
Both places are excellent to visit though worlds apart. My observation of Langkawi was a more eastern tourist destination while Penang was full of westerners, high-rise resorts and general hustle and bustle of a city.
I took a FireFly flight from Langkawi to Penang which was quite cheap and comfortable.
The Malaysian stamp is slightly larger than Singapore stamp, it won't take up more than a quarter of a page, or less than half for entry/exit.
--Russ