I am getting a Shengen VISA here in Singapore, but one requirement is a confirmed ticket and booked hotels.
This may sound to be a silly question, but in case my application gets rejected, can I still refund all that I've payed for?
There's no general answer to your question. For flights, it depends on the ticket. Usually only the most expensive ones are fully refundable. For hotels, you'd have to check that with every hotel you book. The cheaper hotels usually have a less than perfect refund policy.
My recommendation would be to only reserve the hotels.
When you book through Travellerspoint you pay a 10% fee plus a booking fee. Those are non-refundable. I know people who have gotten visa's based upon that. In case you cannot go you loose the 10 % booking fee, but you won't loose all the money the room costs.
A similar deal should be possible for flight tickets. Talk to an experienced travel agent for the flights.
Also check the individual embassies rules. The Austrians will have different rules from the Italians for example.
Depending on the hotels, they may have various booking conditions. Some will give full refunds if you cancel within certain period of time, some will give only partial refunds. And as t_maia pointed out, the TP accommodation system secures a booking on 10% of the amount plus fee, but this would be non-refundable amount. So if you can find hotels which allows full refund for cancellation up to, say, 72 hours, then that will be the way to go in my opinion. Surely you'll know re the visa approval well before 72 hours prior to flight time, especially if you start on the application now.
Re flights, if you go with a travel agent who can hold tickets for you with partial payments, and/or that allows changes/refunds (minus handling charges), that would be ideal. It does mean no booking with, say, Air Asia. Check on the conditions first before committing the purchase.