SIN Transit Hotel : I would defintely try to get a room at the Transit Hotel. There is nothing like a real bed after a long flight but demand for rooms is high and you may have to book way ahead.

I was there just a couple of weeks ago, and there were countless travellers without reservations being turned away. There are some construction work going on in the terminal which goes on in the middle of the night, so dont expect a peaceful night sleep. However unless you are flying F, having a real bed to lie down after a long flight is itself a treat irrespective of whether you are able to sleep or not.

Wifi in Malaysia : Wifi may be available at certain cafes and hotels in KL, but I doubt it is available in rural Pahang. Unless you need to be connected most of the time in KL or your trip is work related, I would not bother adding extra weight to my carry-on if I were you.