Hehe I'm in a similar situation as you, only I not so bad I'll be arriving at 9 or 10pm this friday. Been to SG tons of times but first time driving in lols.

Uncle Google has advised that before entering singapore we need to register/buy an "AutoPass card" (I guess like what stimix said, it is a touch n go kind of card).

Then we got the option to rent an IU to pay "normal" ERP rates but since the IU rental is sgd5/day seems like makes more sense to just pay the flat ERP rate.

Anyway I'm also a bit worried that 10pm reach SG and then the offices all closed and can't purchase the autopass ... then gotta sleep in the car lols. uncle google doesn't help me here