Dunno if Id only go for the F1, Id make it a week if you want to see enough of the place.
Metro system is fantastic, eat/drink in China Town to save a few quid (Tiger beer big bottles are same price as smaller bottles elsewhere for example). 7 Eleven shops are the equivalent to Spar shops over here so while not the cheapest nastiest shops, they are not the most expensive neither.
While there you might as well go and see the zoo its pretty cool with the boat trips etc and night safaris. Taxis arent too expensive as they are subsidised iirc too, £30 gets you practically from one side of the island to the other.
Keep away from Raffles hotel and their Singapore slings unless you have a penchant for spending £100 for a couple of drinks, if so ask for a genuine one not a bottle poured poor alternative. I havent been in a few years now but really want to go back at some point as the kids loved being ther for almost a month and Sentosa Island etc offers plenty to keep anyone busy for a few days alone.
Bear in mind the flights are pretty long, we went from belfast to glasgow to dubai to Columbo, Sri Lanka to Singapore, the stop over in SriLanka wasnt awful (we backhanded the business lounge guy $50 to let us sleep in the lounge overnight and got a decent breakfast the next morning) but on flights in and out of there they spray some sort of anti bacterial dust over everyone once the plane is loaded up and taxiing. Awful stuff.
If you stay over for a day or two in Dubai the Premier Inn just offsite from the Airport is great and pretty cheap and had plenty of facilities, coffee bar, restaurant, attended roof top pools etc. We stayed there and commuted to the Atlantis on the Palm etc for visiting/dinner etc.