1. You won't be able to book a mixed class award on the one ticket so you will need to book SYD-SIN in first class then book SIN-HKT in business class, as Silkair doesn't have first class. This will cost you a lot more miles then SYD-HKT direct but you will only have the business class option for the connecting single award redemption.

If booking a one way SAVER award redemption then you have to pay for a stopover, US$100, only the higher reward redemptions offer a free stopover, whereas all return options give you a free stopover.

I personally would book one way tickets on rewards, as the cost of miles is half that of return unlike paid fares, thus ensuring you have not missed the chance of obtaining the awards redemption going over to HKT.

Hope this helps